jg  .  'V:  . 

International 

Correspondence 

Schools 

SCRANTON,  PA. 

REG  U.S.  PAT.  OFF 

INSTRUCTION  PAPER 

with  Examination  Questions 


FIRST  EDITION 


By-Product  Coking 

860 

SCRANTON,  PA. 

INTERNATIONAL  TEXTBOOK  COMPANY 


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riii  International  Correspondence  Schools 


Copyright,  1906,  by  International  Textbook  Company.  Entered  at  Stationers’ 
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^>o  3V  |^/w 


6?  (o  *2-  ^ 


BY-PRODUCT  COKING 


BY-PRODUCT  COKING  APPARATUS  AND 
PRODUCTS 


RETORT  COKE  OVENS 


PRINCIPLES  OF  BY-PRODUCT  COKING 

1.  Distillation. — When  bituminous  coal  is  placed  in  a 
vessel  that  has  but  one  outlet  and  from  which  air  is  excluded, 
and  the  vessel  is  then  subjected  to  external  heat,  the  volatile 
portions  of  the  coal  will  be  driven  off  in  the  form  of  vapor. 
This  process  is  known  as  the  destructive  distillation  of  coal, 
and  the  vessel  in  which  the  heating  is  accomplished  is  called 
a  retort.  If  the  vapor  that  is  driven  off  is  cooled,  a  por¬ 
tion  of  it  will  be  condensed  into  liquids  while  the  remainder 
will  remain  in  the  form  of  gas.  The  product  remaining  in 
the  retort  is  termed  retort-oven  coke  and  has  value 
both  for  domestic  and  metallurgical  purposes.  The  liquids 
and  gases  that  are  distilled  from  the  coal  are  known  as 
by-products  when  the  distillation  is  conducted  primarily 
for  the  manufacture  of  coke  even  should  they  have  a  greater 
commercial  value  than  the  coke,  and  the  process  is  called 
by-product  coking.  ■  The  coke  is  the  product  generally  sought 
and  is  the  most  valuable  one,  excepting  where  gas  coals 
are  heated  in  small  retorts  for  the  purpose  of  producing  illu¬ 
minating  gas,  in  which  case  the  coke  is  a  by-product. 

2.  Object  of  By-Product  Coking. — When  coking  coal 
in  ordinary  beehive  ovens,  all  the  gases  are  consumed  in 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ALL  RIGHTS  RESERVED 

§71 


2 


BY-PRODUCT  COKING 


§71 


the  oven  to  generate  heat  for  the  coking  process  and  there 
are  consequently  no  products,  other  than  coke,  resulting 
from  the  operation.  When  it  is  understood  that  from  each 
ton  of  coal  having  28  per  cent,  of  volatile  matter  there  can 
be  obtained  approximately  10,000  cubic  feet  of  illuminating 
and  fuel  gas,  5  pounds  of  ammonia  gas,  and  10  gallons  of 
tar,  worth  altogether  at  least  $1,  and  that  34,000,000  tons  of 
coal  are  coked  annually  in  the.  United  States  alone,  the  enor¬ 
mous  loss  resulting  from  beehive-oven  practice  as  compared 
with  by-product  coking  can  readily  be  seen. 

The  manufacture  of  coke  in  by-product  ovens  is  not  a  new 
industry,  as  ovens  of  this  character  were  built  and  the  tar 
and  ammonia  saved  at  Salzbach,  Germany,  as  early  as  1766; 
and  in  1881,  by-product  coking  was  an  established  industry 
in  that  country. 

By-product  ovens  have  replaced  ovens  of  the  beehive  type 
almost  entirely  in  Germany  and  other  European  countries. 
The  reasons  that  they  have  not  been  more  generally  intro¬ 
duced  in  the  United  States  are,  that  their  first  cost  is  at  least 
$4,000  per  oven  as  compared  with  $350  for  a  beehive  oven, 
thus  necessitating  a  much  larger  outlay  to  establish  a  coke 
plant;  that  it  is  necessary  for  them  to  be  so  situated  that  the 
waste  gas  can  be  marketed  or  utilized  to  advantage;  that 
royalties  are  demanded  by  the  owners  of  the  patents  in  this 
country;  and  also  that  there  has  been  an  uncertainty  in 
regard  to  the  market  for  the  by-products — tar  and  ammonia. 

3.  Coke  Output  From  Retort  Ovens. — In  addition  to 
the  saving  in  by-products,  retort  ovens  give  an  increased 
output  in  coke  over  the  beehive  oven.  This  is  due  to  the 
fact  that  there  is  loss  of  fixed  carbon  in  beehive  ovens, 
owing  to  the  burning  of  some  of  the  coke  during  the  process 
of  coking,  this  loss  being  greater  in  coals  low  in  volatile 
matter  than  in  those  higher  in  volatile  matter.  Also,  in  the 
retort  process,  a  portion  of  the  volatile  hydrocarbons  are  said 
to  be  fixed — that  is,  decomposed — so  that  some  of  their  car¬ 
bon  is  deposited  on  the  coke  produced  from  the  fixed  carbon 
of  the  coal,  thus  yielding  from  1  to  2  per  cent,  more  coke  than 


§71 


BY-PRODUCT  COKING 


3 


would  be  expected  from  a  calculation  based  on  the  amount  of 
fixed  carbon  and  ash  in  the  coal.  The  by-product  oven  being 
constructed  on  the  retort  plan  and  keeping  the  coal  from 
coming  in  contact  with  but  little  of  the  oxygen  of  the  air, 
most  of  the  fixed  carbon  in  the  coal  is  retained. 

4.  Coals  Suited  for  By-Product  Coke  Ovens. 
Usually,  coking  coals  low  in  volatile  hydrocarbons  produce 
a  hard  strong  coke  in  by-product  ovens,  while  those  high  in 
volatile  matter  produce  coke  that  has  a  soft  spongy  struc¬ 
ture.  Coals  containing  between  15  and  20  per  cent,  of  vola¬ 
tile  hydrocarbons  can  be  coked  without  appreciable  loss  of 
fixed  carbon  in  a  by-product  oven.  The  greater  the  percent¬ 
age  of  volatile  matter  in  a  coal,  the  greater  will  be  the  yield 
of  gas,  tar,  and  ammonia;  but  when  there  is  over  28  per 
cent,  of  volatile  matter  in  a  coal,  it  does  not  usually  give  a 
first-class  coke.  Although  the  chemical  analysis  of  a  coking 
coal  will  indicate,  to  some  degree,  the  chemical  composition 
and  probable  quantity  of  coke,  gas,  and  by-products  that 
may  be  obtained  from  it,  there  are  so  many  inconsistencies 
found  in  results,  that  these  data  can  be  determined  with 
certainty  only  by  actual  test.  It  may  be  stated  that  a  coal 
that  will  admit  of  coking  in  the  beehive  oven  will  offer 
no  particular  difficulty  to  treatment  in  the  by-product  oven; 
and  it  is  claimed  that  some  coals  that  will  not  coke  in  the 
beehive  oven  call  be  successfully  coked  ia  the  by-product 
oven.  It  is  maintained  by  some  that  coking  coals  con¬ 
taining  as  high  as  31  per  cent,  of  volatile  matter  yield 
coke  of  a  better  structure  when  coked  in  by-product 
ovens  than  when  coked  in  beehive  ovens,  owing  to  the 
increased  depth  of  the  charge  and  the  increased  weight  on 
the  lower  part  of  the  charge  in  the  by-product  ovens.  This 
may  be  true  in  a  measure  for  all  the  coal  below  18  inches 
from  the  top,  but  since  the  upper  18  inches  of  the  charge  is 
also  dense,  it  is  probable  that  the  slow  dry  heat  has  much 
to  do  with  improving  the  structure  of  the  coke. 

5.  Relative  Costs  of  Beehive  and  By-Product  Proc¬ 
esses. — Table  I  gives  a  comparison  by  a  manufacturer  of 


4 


BY-PRODUCT  COKING 


§71 


by-product  ovens  of  the  relative  costs  and  results  in  making 
coke  in  beehive  and  by-product  ovens,  no  account  being 
taken  of  any  royalties  charged  on  the  by-product  ovens. 


TABLE  I 

RELATIVE  COST  OF  COKE  MADE  IN  BEEHIVE  AND  IN 
BY-PRODUCT  COKE  OVENS 


S 

c 

V 

*0 

C 0 

a 

0 

aS  cfl 

c 

0 

ID'S 

0 

c  c 

0  0 
bh 

(Sj 

®  0. 
5?  o> 

p 

a 

c  □ 

.2  S 

(U 

£ 

<D 

a 

M 

O 

O 

O 

Type  of  Oven 

Cost  per  Oven 

'aily  Output,  Net  T 
2,000  Pounds 

O  0) 

</3  O 

co 

o§ 

l! 

|8 
p  0 

Total  Cost  of  Pla 

ads  of  Coke  Obtain 
100  Pounds  of  Coa 

®  "5 

M  U 

_  <D 

.2  a 

73£ 

0*. 

O 

M-l  0) 

O 

wO 

u* 

®  be 
ftc 

II 

73  y 

1-,  C 

Pi  - 

°o 

73° 

0  Sj 

a  0 

<u  « 

073 

c  0 

It 

id  "S 

lue  of  By-Products 

Ton  of  Coke 

C 

O 

t-i 

0) 

S3 

0 

0 

0 

Q 

S  M 

c 

0 

PU 

0 

O 

Vi  ^ 

0  0 

0 

c 

cfl 

> 

75 

Beehive  .  . 

$  325 

2.00  j 

500 

$162,500 

66 

$1.50 

$.46 

$.05 

$2.01 

By-product 

4,000 

4-25 

235 

940,000 

7i 

I.41 

.70 

•31 

$1.41 

I. OI 

These  figures  are  made  on  the  assumption  of  the  following 
returns  per  ton  of  coal: 

5  per  cent,  tar  =  10  gallons  at  2j  cents  ...  $  .25 
1  per  cent,  ammonia  sulphate  =  20  pounds  at 

2i  cents . 50 

3,500  cubic  feet  of  gas  at  7.14  cents  per  1,000 
cubic  feet . 25 

Total  . $1.00 


BY-PRODUCT  COKING  PLANTS 

6.  Location  of  By-Product  Plants. — By-product  plants 
are  usually  located  near  to  where  the  coke  is  to  be  consumed, 
or  where  there  is  a  market  for  the  by-product  gas,  but  railroad 
and  water  freights  on  coal  and  coke  must  be  considered  in 
settling  on  a  location.  Coal  is  a  commodity  easily  handled, 
and  can  be  shipped  with  but  little  loss.  Coke,  on  the  other 
hand,  is  bulkier,  must  be  handled  with  more  care  and,  besides, 
it  deteriorates  by  exposure,  particularly  when  shipped  by 


§71 


BY-PRODUCT  COKING 


5 


water.  The  railroads  recognize  these  facts  and  the  freight 
rates  for  coal  are  usually  enough  below  those  for  coke  to 
equalize  the  two.  The  disposal  of  the  gas  is  also  a  matter 
demanding  careful  consideration;  and  in  the  case  of  a  plant 
to  make  blast-furnace  coke,  when  proximity  to  a  labor  center 
is  necessary,  the  market  for  the  surplus  gas  makes  a  by-prod¬ 
uct  oven  plant  adjoining  the  blast  furnace  a  very  attractive 
proposition.  The  recent  developments  in  piping  gas  long 
distances  under  pressure  have  somewhat  extended  the  limits 
of  the  problem,  but  in  general  the  greatest  advantage  is 
gained  by  shortening  the  coke  haul  as  much  as  possible.  If 
domestic  coke  is  to  be  the  product,  the  need  for  locating  near 
the  market  is  equally  apparent,  particularly  as  the  gas  from 
this  type  of  plant  is  especially  adapted  to  city  distribution. 
The  disposal  of  the  tar  and  ammonia  is  not  so  difficult  a 
matter.  The  demand  for  tar  is  now  quite  extensive;  and  by 
means  of  tank  cars  the  supply  can  be  easily  marketed  from 
any  desirable  location  for  a  by-product  plant.  Ammonia,  in 
the  form  of  strong  crude  liquor,  is  also  easily  shipped,  but 
there  is  less  likely  to  be  as  strong  a  local  demand  for  it  as  for 
tar.  In  case  ammonium  sulphate  is  to  be  made,  care  must  be 
taken  to  have  a  source  of  sulphuric  acid  supply  assured. 
The  other  considerations,  character  of  ground,  proximity  of 
water  for  boilers  and  condensation,  freedom  from  floods  and 
freshets,  etc.  are  common  to  most  industrial  plants,  and  need 
not  be  further  dealt  with  here. 

7.  General  Arrangement  of  By-Product  Coke-Oven 
Plant. — A  general  idea  of  the  requirements  of  a  by-product 
coke-oven  plant  may  be  had  from  Fig.  1,  which  is  a  view  of 
the  plant  of  the  New  England  Gas  and  Coke  Company  at 
Everett,  Massachusetts.  This  plant  was  designed  to  coke 
coal  from  Nova  Scotia;  and  as  there  is  a  ready  market  for  a 
large  amount  of  illuminating  gas  in  Boston  and  other  near-by 
cities,  especial  attention  has  been  paid  in  its  design  and 
operation  to  the  production  of  gas  for  illuminating  purposes. 

The  coal  for  this  plant  is  brought  from  Nova  Scotia  by 
steamship  and  is  unloaded  into  a  bin  a.  It  is  then  raised  up 


6 


Fin 


§71 


BY-PRODUCT  COKING 


7 


the  inclines  b  in  cars  and  dumped  into  the  bins  c ,  or  else  con¬ 
veyed  over  the  bridge  d  to  bins  e.  The  coal  is  drawn  into 
larries  from  these  bins,  carried  to  the  ovens,  and  discharged 
into  them,  each  bin  supplying  coal  for  two  blocks  of  ovens. 
There  is  also  a  coal  stock  pile  from  which  to  draw  in  case  of 
necessity.  The  traveling  crane  h  transfers  the  coal  from  the 
stock  pile  to  conveyers,  which  carry  it  to  bins  e  for  the  second 
row  of  ovens;  it  is  also  conveyed  across  the  bridge  d  to  coal 
bins  c  for  the  first  row  of  ovens. 

Retort  ovens  are  long  and  narrow  chambers  from  which 
the  coal,  when  it  is  coked,  may  be  pushed  by  a  machine  /, 
termed  a  coke  pusher ,  into  coke  pans  k ,  where  it  is  quenched 
with  water.  The  coke  is  next  loaded  into  cars  and  shipped 
to  consumers  or  else  stored  for  the  local  trade.  In  this 
plant,  there  are  eight  blocks  of  ovens,  each  surmounted  by  a 
cantilever  bridge  /  on  which  the  larries  run  to  and  fro  in 
carrying  coal  from  the  coal  bins  to  the  ovens.  A  battery  of 
by-product  ovens  usually  includes  about  fifty  ovens,  as  this 
number  can  be  easily  charged  from  one  coal  bin. 

After  the  ovens  are  charged,  all  openings  are  sealed  air¬ 
tight,  except  those  on  top  that  are  connected  by  pipes  with 
gas  mains  and  through  which  the  volatile  part  of  the  coal 
escapes  when  the  walls  of  the  ovens  are  heated  with  gas.  The 
tar  contained  in  the  gas  is  removed  in  the  condensing  house  m 
and  the  ammonia  in  the  ammonia  house  n.  The  first  gases 
given  off  by  the  coal  are  rich  in  illuminants,  and  are  saved  in  the 
tank  o;  the  balance  of  the  gases  are  burned  to  heat  the  ovens 
and  the  products  of  combustion  are  drawn  off  and  up  the  high 
chimneys  p.  The  plant  also  includes  a  powerhouse  r ,  and  a 
small  plant  t  for  treating  the  tar,  besides  the  numerous  small 
buildings  accessory  to  so  extensive  a  plant. 


8 


BY-PRODUCT  COKING 


§71 


§71 


BY-PRODUCT  COKING 


9 


BY-PRODUCT  COKE  OVENS 
8.  Classification  of  By-Product  Coke  Ovens. — While 
there  are  a  number  of  types  of  by-product  coke  ovens  in  use 
in  Europe  only  two  of  these  types  have  been  adopted  in  the 
United  States;  these  are  the  Otto-Hoifman,  or  vertical-flue, 
oven,  and  the  Semet-Solvcty ,  or  horizontal-flue,  oven.  These 
two  types  have  been  improved  and  adapted  to  meet  con¬ 
ditions  as  they  exist  in  America.  Each  by-product  coke- 
oven  plant  of  whatever  type  so  far  erected  in  the  United 
States  differs  from  the  plants  previously  erected  in  a  number 
of  particulars  that  were  supposed  to  be  improvements.  As 
many  of  these  changes  have  not  proved  advantageous,  they 
have  been  abandoned;  therefore,  only  such  particulars  as  are 
apparently  satisfactory  will  be  mentioned. 


OTTO-IIOFFMAN  OVENS 

9.  German  Otto-Hoffman  Oven. — Fig.  2  is  an  illustra¬ 
tion  of  a  block,  or  battery,  of  Otto-Hoffman  by-product 
coke  ovens  in  Germany.  There  are  doors  a  at  each  end  of 
the  oven  and  when  the  coking  operation  is  complete  these 
doors  are  raised  by  a  crab  winch  b  mounted  on  wheels,  so 
that  it  may  be  moved  from  oven  to  oven  on  tracks  c.  The 
doors  are  of  cast  iron  and  firebrick,  and  when  raised  the 
coke  is  pushed  from  the  oven  on  to  the  yard,  where  it  is 
quenched  by  streams  of  water  as  shown.  After  the  coke  has 
been  removed  from  the  retort,  the  doors  are  immediately 
lowered  and  luted  with  clay  to  make  the  retort  air-tight. 
After  the  coke  is  quenched,  it  is  loaded  into  barrows  d  and 
dumped  into  the  railroad  cars  e. 

The  gas  coming  off  from  the  coal  is  conducted  by  the  off¬ 
takes  /  to  a  central  gas  main  that  is  raised  quite  high  above 
the  ovens  in  order  that  the  gas  flowing  through  it  may  be 
cooled  by  air  and  not  absorb  radiated  heat  from  the  ovens. 

10.  American  Otto-Hoffman  Oven. — Fig.  3  illustrates 
an  Otto-Hoffman  by-product  oven  plant  at  Johnstown,  Penn¬ 
sylvania.  The  doors  a  in  this  case  are  raised  by  a  block  and 


§71 


BY-PRODUCT  COKING 


11 


fall  attached  to  a  gantry  crane  b  and  operated  by  hand  or 
electric  power.  The  latest  innovation  for  quenching  coke  as 
it  comes  from  the  oven  and  then  loading  it  into  cars  is 
shown  at  c.  It  consists  of  an  iron  box  resting  on  a  frame 
that  is  mounted  on  wheels,  which  run  on  a  track  as  shown. 
The  entire  structure  is  so  arranged  that  it  may  be  moved  at 
will  from  oven  to  oven  by  its  own  machinery.  The  coke  is 
pushed  directly  from  the  oven  into  this  quencher  car,  which 
is  constructed  with  hollow  cast-iron  sides,  thus  forming  a 
receptacle  around  the  car  into  which  water  is  pumped  until  it 
flows  over  the  top  of  the  inner  wall  on  to  the  coke.  The 
steam  evolved  acts  as  a  dryer  while  the  surplus  steam  passes 
out  of  the  stacks  d.  This  quencher  car  is  used  when  it  is 
desired  to  give  the  coke  a  silvery  appearance  similar  to  that 
shown  by  beehive  coke  that  has  been  watered  inside  the 
oven.  Except  in  appearance,  there  is  probably  no  improve¬ 
ment  in  coke  quenched  in  cars  over  that  quenched  in  pans 
and  on  the  yard.  Probably,  there  is  a  saving  in  time  of 
watering  by  the  use  of  quencher  cars. 

The  quencher  cars  are  supplied  with  doors  that  are  opened 
as  soon  as  the  coke  is  cooled  and  the  contents  discharged 
into  the  railroad  car  e. 

The  mechanism  for  moving  the  cooled  coke  from  the 
quencher  car  consists  of  a  heavy  chain  placed  on  the  floor 
and  extending  through  each  door  and  outside  underneath  the 
floor.  This,  when  moved  by  a  motor,  breaks  up  the  coke 
and  discharges  it  into  the  coke  car  e. 

The  high  stacks  /  carry  off  the  waste  gases  from  the  ovens 
and  assist  the  oven  draft,  which  is  usually  aided  by  an 
exhaust  fan  placed  at  the  end  of  an  oven  battery.  The  waste 
gases  for  heating  the  oven  flues  enter  through  the  gas 
pipes  g. 


11.  Otto-Hoffman  Coke-Oven  Section. — Fig.  4 
shows  a  sectional  elevation  of  a  recent  type  of  Otto-Hoffman 
oven.  The  coal  for  the  ovens  is  dumped  from  the  cars  a 
into  a  track  hopper  b  below  the  tracks,  from  which  it  is  carried 
by  elevators  running  inside  the  housing  c  to  the  top  of  the 


12 


§71 


BY-PRODUCT  COKING 


13 


bin  d  and  there  discharged.  The  coal  is  drawn  from  the  bin  d 
through  gates  and  spouts  e  into  the  larry  /.  The  larry  in 
this  case  consists  of  five  hoppers  g,  each  having  a  spout  to 
discharge  the  coal  into  the  ovens.  The  whole  is  held  by  a 
framework  mounted  on  a  truck  that  moves  on  the  rails  h 
at  each  end  of  the  ovens.  The  hoppers  g  are  discharged 
through  trunnel  heads  i  in  the  top  of  the  oven;  and  as  the 
coal  is  thus  distributed  the  entire  length  of  the  retorts  j, 
little  labor  is  required  to  level  it.  This  leveling  is  frequently 
done  by  a  rake  k,  which  is  moved  back  and  forward  by  suit¬ 
able  gears  in  connection  with  the  coke  pusher  /.  Two  of 
the  larry  funnels  discharge  into  pipes  m  through  which  the 
gas  passes  out  of  the  oven  and  which  connect  with  the  gas 
mains  o ,  o'.  The  object  of  the  two  gas  mains  is  to  keep  the 
rich  gas  that  comes  off  from  the  coal  first  from  the  poorer 
gas  that  comes  off  later.  This  might  be  done  by  a  system 
of  valves  as  readily  from  one  main  as  from  two,  but  there  is 
an  advantage  in  having  two  mains  to  these  ovens,  since  the 
heat  is  applied  alternately  to  one  end  and  then  to  the  other 
end  of  the  retort.  After  the  coal  is  coked,  it  is  pushed  out 
of  the  retort  j  by  a  pusher  /  that  is  operated  by  machinery 
located  on  the  framework  as  shown.  This  frame  runs  on  a 
track  pp  so  that  it  can  be  placed  opposite  any  oven.  The 
coke  is  pushed  into  the  quenching  car  q  similar  to  that  shown 
in  Fig.  3.  The  water  for  quenching  the  coke  flows  through 
the  ditch  r  from  which  it  is  drawn  by  the  pump  5.  While  a 
piston  pump  is  sometimes  used  for  this  purpose,  it  is  cus¬ 
tomary  to  use  a  centrifugal  pump  as  it  will  deliver  a  larger 
quantity  of  water  under  the  small  head,  and  because  of  its 
comparative  simplicity  in  construction  and  light  weight.  The 
gas  for  heating  the  ovens  comes  from  the  gas  tank  through 
the  pipes,  as  t  or  t’ ,  at  one  end  of  the  oven,  and  enters  the 
combustion  chambers  under  the  oven  flues,  where  it  mixes 
with  the  air  from  the  air  chambers  u ,  which  has  been  heated 
by  passing  through  the  checkerwork  v.  The  burning  gases 
then  pass  up  vertical  flues  between  the  ovens  into  a  horizontal 
flue  running  lengthwise  of  the  oven,  down  other  vertical  flues 
at  the  other  end  of  the  oven  into  the  chamber  u' ,  then  out 

151—23 


I3| 


14 


BY-PRODUCT  COKING 


§71 


through  the  checkerwork  v '.  After  the  current  of  gas  has  been 
passing  in  this  direction  for  a  certain  time,  until  the  air  pass¬ 
ing  through  v  has  cooled  the  checkerwork,  the  direction  of 
the  current  of  burning  gas  is  changed  by  means  of  suitable 
valves,  as  is  fully  explained  later.  The  passage  of  the  hot 
waste  gases,  after  leaving  the  oven  alternately  through  brick 
checkerwork  v  and  v'  on  the  way  to  the  stack,  heats  the 
bricks  and  when  the  gas  and  air-currents  are  reversed  the 
heat  from  the  bricks  is  given  up  to  the  air  before  it  meets 
the  gas.  This  brickwork  is  called  a  regenerator ,  or  some¬ 
times  a  hot-blast  stove ,  and  may  be  located  in  various  places, 
sometimes  at  each  side  of  the  oven  and  sometimes  directly 
under  the  center  of  the  oven. 

The  gas  used  for  heating  the  oven  is  sometimes  the  last 
part  of  the  gas  given  off  in  the  process  of  coking  and  from 
which  the  by-products  tar  and  ammonia  have  been  removed, 
but  often  producer  gas  is  used  for  this  purpose. 


OTTO-HOFFMAN  OVEN  DETAILS 

12.  Retort. — Retort  coke  ovens  are  constructed  so 
that  the  coal  is  not  in  direct  contact  with  the  flame  that  fur¬ 
nishes  the  heat  for  coking.  The  sides,  walls,  and  bottoms  of 
the  retorts  are  built  of  firebrick  or  silica  brick.  The  side 
walls  are  constructed  of  small  bricks  having  a  square  section 
and  bonded  together  so  as  to  make  a  series  of  vertical  flues. 
As  it  is  necessary  that  the  retorts  should  be  gas-tight,  the 
joints  are  made  as  true  as  possible  and  all  the  bricks  are 
ground  on  carborundum  wheels  to  a  prescribed  thickness. 
This  method  not  only  adds  to  the  tightness  of  the  wall,  but 
is  also  much  cheaper  than  the  usual  method  of  chipping  and 
rubbing  bricks  by  hand  to  give  them  smooth  surfaces. 

The  heat  derived  from  the  combustion  of  the  gas  in  these 
flues  is  transmitted  through  the  retort  walls  to  the  coal  inside 
the  retort  and  drives  off  the  volatile  matter,  which  is  carried 
off  in  pipes  to  the  by-product  plant  and  there  treated,  as  will 
be  described  in  detail  later. 

An  Otto-Hoffman  retort  is  shown  in  longitudinal  section 
in  Fig.  5,  and  Fig.  6  is  a  section  alongside  Fig.  5,  through 


§71 


BY-PRODUCT  COKING 


15 


Fig.  5 


Fig.  6 


16 


BY-PRODUCT  COKING 


71 


the  combustion  chambers.  The  rectangular  retort  a  is 
walled  with  silica  firebrick  on  each  side;  the  floor  b  that 
separates  the  retort  chamber  from  the  air  chambers  c  and  d 
is  of  fireclay  tile,  and  the  roof  e  above  the  retort,  of  fireclay 
bricks.  The  top  of  the  retort  has  five  trunnel  heads  /  provided 
with  suitable  covers  to  make  them  air-tight.  In  some  cases, 
the  off-takes  g  are  also  used  as  trunnels  through  which  the 
ovens  are  charged,  as  was  explained  in  connection  with  Fig.  4; 
in  other  cases,  they  have  no  connection  with  the  trunnel  heads. 
The  oven  walls,  front  and  back,  are  held  together  by  tie- 
rods  h  that  are  passed  through  iron  castings  i  and  held  in 
place  by  nuts  j.  These  castings  serve  as  buckstaves,  and 
are  sometimes  made  long  enough  above  the  ovens  to  carry 
a  track  on  which  the  door-hoisting  winch  runs.  The  buck- 
staves  also  act  as  door  slides  and  hold  the  brace  bars  and 
wedges  employed  to  assist  in  making  the  door  joints  air-tight. 

13.  Size  of  Retort. — The  retort  has  not  been  changed 
in  shape  in  the  several  modifications  of  the  Otto-Hoffman 
oven,  but  the  dimensions  have  been  varied  as  follows:  width, 
from  15-8  inches  to  22  inches;  height,  from  5  feet  6.  inches  to 
6  feet  6  inches;  and  length,  from  30  feet  to  33  feet.  The 
Camden,  New  Jersey,  plant,  which  is  one  of  the  latest  con¬ 
structions,  has  retorts  17  inches  wide,  6  feet  6  inches  high, 
and  33  feet  long.  The  retorts  are  placed  side  by  side,  sepa¬ 
rated  by  a  flue  that  makes  them  2  feet  lOi  inches  from 
center  to  center.  They  are  charged  with  5  tons  of  coal  and 
produce,  from  this  charge,  about  3.75  tons  of  coke. 

A  retort  cannot  be  filled  with  coal,  as  a  coking  coal  swells 
during  coking  and  does  not  settle  down  again  until  most  of 
the  volatile  matter  has  been  expelled. 

14.  Air  Chambers. — Directly  beneath  the  floor  of  each 
oven  are  the  two  air  chambers  c,  d  connected  by  flues  k ,  l 
with  the  regenerators  m,  m' .  These  air  chambers  deliver 
heated  air,  through  the  port  holes  o,  o',  to  the  combustion 
chambers  n,n’,  Fig.  6,  situated  parallel  to,  and  on  each  side 
of,  the  air  chambers.  A  partition  p  separates  the  air  chambers 
from  the  air  chamber  d  and  also  the  combustion  chamber  ?i 


§71 


BY-PRODUCT  COKING 


17 


from  the  combustion  chamber  n' .  If  the  air  is  admitted  to 
the  air  chambers  c  at  k ,  Fig.  5,  it  will  pass  through  the  port 
holes  o  into  the  combustion  chamber  n ,  Fig.  6,  and  thence  up 
through  the  retort  flues  r  and  down  through  the  flues  r'  to 
the  combustion  chamber  n '  before  it  can  pass  through  the 
port  holes  o' ,  Fig.  5,  into  the  air  chamber  d  and  to  the  outlet 
flue  /.that  conducts  it  to  the  regenerator  in' ,  where  it  gives 
up  its  heat  to  the  checkerwork.  After  the  latter  becomes 
heated  to  the  proper  temperature,  the  air-current  is  reversed 
and  the  regenerator  m  brought  up  to  the  required  temperature. 

15.  Combustion  Chambers.— The  gas  for  heating  the 
retorts  is  admitted  through  the  nozzles  q,  q'  to  the  combus¬ 
tion  chambers  n,  Fig.  6,  which  are  the  counterparts  of 


Fig.  7 


the  air  chambers  c ,  d ,  Fig.  5,  and  have  similar  partitions  p 
to  separate  them.  If  the  gas  and  the  air  for  combustion  are 
admitted  to  the  combustion  chamber  n  corresponding  to 
the  air  chamber  c ,  the  products  of  combustion  travel  to 
the  combustion  chamber  corresponding  to  d  and  so  to  the 
regenerator  m1 . 

Fig.  7  shows  the  combustion  chambers  n  separated  length¬ 
wise  from  the  combustion  chambers  n'  by  the  partition  p , 
before  the  retort  floors  b,  Fig.  5,  are  put  on.  The  air  cham¬ 
bers  c,  d  are  between  the  combustion  chambers  and  are  also 
separated  by  the  partition  p. 

16.  Vertical  Flues  in  Retort  Side  Walls. — After  the 
gases  ignite  in  the  combustion  chamber,  they  pass  upwards 
into  a  series  of  vertical  flues  r,  r'  as  shown  in  the  section, 
Fig.  6.  These  flues  are  between  the  side  walls  of  two  adjacent 


1! 


§71 


BY-PRODUCT  COKING 


19 


retorts  and  terminate  in  a  horizontal  flue  s.  The  combustion 
of  the  gas  takes  place  alternately  in  the  combustion  cham¬ 
bers  n,  n'  on  opposite  ends  of  the  retorts.  Assume  that  com¬ 
bustion  is  occurring  in  the  chamber  n ,  then  the  flames  will 
pass  up  flues  r  into  the  horizontal  flue  s,  and  from  the  latter 
down  the  flues  r1  into  the  combustion  chamber  n' .  From  this 
chamber,  the  waste  gases  of  combustion  will  pass  through 
ports  o' ,  Fig.  5,  into  air  chamber  d  to  flue  /  through  regener¬ 
ator  m'  to  flue  u  and  thence  to  the  stack.  After  the  gas  has 
burned  until  the  bricks  in  the  regenerator  in'  have  become  so 
hot  that  the  waste  gases  escaping  to  the  stack  register  500°  F., 
the  gas  and  air  are  turned  off  from  this  end  of  the  oven  and 
turned  into  the  other  end.  The  current  will  now  be  reversed 
and  the  hot  gases  will  flow  in  the  opposite  direction  through 
the  flues  and  out  through  flue  k  through  the  regenerator  m 
and  the  flue  t  to  the  stack. 

17.  Retort  Foundations. — The  retorts  are  supported 
on  massive  foundations  constructed  of  concrete  and  brick 
masonry.  Fig.  8  shows  the  foundations  up  to  the  combustion- 
chamber  floor  for  an  oven  similar  in  its  arrangement  to  that 
shown  in  section  in  Figs.  5  and  6.  The  outer  walls  a  are 
entirely  concrete  while  the  inner  walls  b  are  concrete  below 
and  brick  masonry  above.  In  order  to  prevent  too  much 
heat  being  transmitted  through  the  floor  of  the  combustion 
chambers  to  the  masonry,  a  series  of  cooling  flues  c  are 
introduced,  which  extend  the  length  of  the  oven  battery. 
Between  the  piers  b  and  the  foundation  walls  a ,  the  flues  s 
are  constructed  in  which  the  regenerators  are  built.  These 
flues  are  of  fire-brick,  as  they  conduct  the  hot  gases  that 
leave  the  oven  at  a  temperature  of  500°  F.  to  the  stack. 
Foundations  of  the  kind  illustrated  are  expensive  and  must 
be  carefully  constructed  so  that  no  settling  will  occur  and 
crack  the  walls  of  the  retorts.  At  each  end  of  the  battery, 
there  are  sometimes  heavy  end  walls  to  resist  expansion,  but 
as  these  walls  are  not  considered  adequate  to  prevent  dam¬ 
age  to  a  battery  of  fifty  ovens  expansion  spaces  are  left  at 
several  points  in  the  length  of  a  block  of  ovens. 


20 


BY-PRODUCT  COKING 


71 


Another  form  of  foundation  is  shown  in  Fig-.  4  in  which 
the  superstructure  is  supported  on  a  steel  framework,  which, 
in  turn,  rests  on  two  side  piers  and  one  central  pier. 

18.  Regenerators. — The  regenerators  m,  m',  Figs.  5 
and  6,  and  v,  v',  Fig.  4,  are  so  called  because  the  waste  heat 
given  off  by  the  combustion  of  waste  gases  as  they  pass 
to  the  stack  is  partly  absorbed  by  the  checkerwork  compo¬ 
sing  the  regenerators  and  is  returned  by  the  air  passing 
through  the  flues  to  add  to  the  heat  of  the  gases  when  they 
-  are  burned  in  the  combustion  chamber  of  the  oven.  If,  in 
Figs.  5  and  6*,  air  is  admitted  at  t  and  allowed  to  pass 
through  the  regenerator  m,  the  flue  k ,  and  air  chamber  c,  into 
the  combustion  chamber  n  and  flues  r  and  the  hot  waste 
gases  of  combustion  are  allowed  to  pass  down  through  /, 
n' ,  d,  l  and  the  regenerator  m'  into  the  flue  u,  the  waste  gases 
will  deliver  up  considerable  of  their  heat  to  the  first  bricks 
they  come  in  contact  with,  the  heat  decreasing  in  intensity 
toward  the  bottom  of  the  regenerator.  On  the  reversal  of 
the  air-current,  so  that  air  passes  up  through  m' ,  /,  d ,  n\ 

and  r'  and  down  through  r,  n,  c,k,m,  and  t}  the  cool  air  will 
become  heated  in  passing  through  m'\  and  being  hot  before 
the  combustion  of  the  gases  takes  place  will  increase  the 
heat  of  the  gases  resulting  from  the  combustion. 

By  reversing  the  air  and  gas  currents  every  30  minutes,  the 
retort  heat  is  kept  fairly  uniform  and  the  regenerators  become 
hotter  and  hotter  as  coking  proceeds.  To  increase  the  tem¬ 
perature  of  the  air  before  entering  the  regenerators,  it  is 
admitted  through  the  arches  v,  w,  and  x,  Figs.  6  and  7,  in  the 
substructure;  and  after  passing  the  entire  length  of  the  oven 
block,  is  drawn  back  by  a  fan  through  the  flues  y  and  then 
forced  by  the  fan  into  the  flues  t  or  u  and  the  regenerator,  and 
on  to  the  combustion  chambers.  The  air  passing  through  the 
flues  y  cools  the  bottom  of  the  retort  floor  and  keeps  it  from  get¬ 
ting  too  hot;  and  at  the  same  time  the  air  is  preheated  to  800° 
F.,  and  then,  by  passing  through  the  regenerator,  to  1,500°  F. 

Should  this  process  continue  without  interruption,  the 
ovens  would  become  so  hot  that  they  would  melt;  but  the 


§71 


BY-PRODUCT  COKING 


21 


temperature  is  regulated  by  the  absorption  of  heat  by 
the  coal  during  coking  and  by  radiation  and  cooling  during 
the  time  the  coke  is  being  pushed  from  the  oven  and  a  new 
charge  is  being  put  in.  Hence,  the  temperature  in  the  oven 
probably  does  not  exceed  at  any  time  2,500°  F. 

19.  Regulating  the  Heat. — The  stack  into  which  the 
waste  gases  finally  escape  is  usually  placed  at  the  end  of  a 


block  of  ovens,  though  it  may  be  at  one  side,  as  shown  in 
Fig.  3.  Fig.  9  is  a  plan  showing  the  arrangement  of  piping 
at  the  stack  end  of  a  block  of  ovens  for  reversing  the  air  and 
gas  currents.  A  chamber  a  covered  by  a  hood  is  connected 
with  the  flues  t  and  u  of  the  regenerators;  a  third  flue  b  leads 
to  the  stack.  The  air  for  combustion  is  blown  by  a  fan  c 
through  pipe  d  alternately  to  the  right  and  left  flues  t  and  u , 
as  the  temperature  demands,  by  shifting  the  valves  e  in 


22 


BY-PRODUCT  COKING 


§71 


the  hood  covering  the  chamber  a.  The  gas  for  heating  the 
ovens  comes  through  the  main  /  and  is  directed  to  the 
mains  z ,  z\  one  on  each  side  of  the  block  of  ovens  by 
the  valve  g.  When  the  gas  is  going  through  the  right-hand 
main  z'  to  the  combustion  chamber  n\  it  is  cut  off  from  the 
left-hand  main  z  leading  to  combustion  chamber  n ,  and  vice 
versa.  Assuming  that  combustion  of  gas  is  occurring  in  the 
chamber  n\  the  products  of  combustion  will  pass  out  through 
the  left-hand  flue  /,  and  passing  into  the  chamber  a  will  be 
guided  by  the  valve  hood  //,  Fig.  10,  into  the  stack  flue  b. 
As  soon  as  the  pyrometer,  or  heat-measuring  instrument, 
located  at  k  in  flue  b ,  Fig.  9,  registers  500°  F.,  an  electric 


alarm  bell  indicates  that  the  air  and  gas  currents  should  be 
reversed.  If  the  current  is  not  reversed,  the  intake  gener¬ 
ator  will  continually  become  cooler  and  the  waste  gases 
become  hotter  and  hotter,  thus  causing  a  loss  of  heat  through 
the  stack.  The  attendant  therefore  throws  the  gas  valve  g 
and  sends  the  gas  through  the  left-hand  gas  main  z  to  the 
combustion  chambers  n  of  the  entire  block  of  ovens.  He 
also  throws  over  the  lever  /,  Fig.  10,  which  places  the 
hood  h  in  the  position  h'  as  indicated  by  the  dotted  lines  and 
thus  reverses  the  combustion  air-current  and  the  direction 
in  which  the  waste  gases  travel  to  the  stack  flue  b.  This 
system  produces  a  remarkably  uniform  heat  in  the  ovens, 
which  is  a  matter  of  importance,  as  irregular  heating  will 


§71 


BY-PRODUCT  COKING 


23 


retard  coking  operations  in  the  cooler  parts  of  the  retorts 
and  cause  overheating  in  other  parts.  The  supply  of  gas 
and  air  to  each  individual  combustion  chamber  having  once 
been  determined,  and  the  ports  k  and  /,  Fig.  5,  regulated  for 
the  necessary  supply  of  air  to  burn  the  gas  coming  through 
gas  nozzles  q  and  q',  the  two  are  never  changed. 

20.  Economy  of  the  Regenerator. — From  an  analysis 
of  the  gas  used  for  heating  the  retorts  of  an  oven,  the 
value  of  the  regenerating  system  may  be  calculated.  An 
analysis  of  the  Everett,  Massachusetts,  oven-heating  gas 
is  as  follows: 

Per  Cent. 


Marsh  gas,  CH< .  29.2 

Hydrocarbons  other  than  marsh  gas  ....  2.4 

Hydrogen,  H . 50.5 

Carbon  monoxide,  CO .  6.3 

Carbon  dioxide,  C02 .  2.2 

Oxygen,  O .  .3 

Nitrogen,  N .  9.1 

Total . MO 


It  was  found  that  1  cubic  foot  of  this  gas  requires  4.54 
cubic  feet  of  air  for  complete  combustion;  hence,  5,000  cubic 
feet  of  gas  requires  22,700  cubic  feet  of  air.  This  air,  at 
sea  level,  weighs  1,832  pounds  with  the  mercury  in  the  bar¬ 
ometer  standing  at  29.92  inches  and  the  temperature  32°  F. 
The  specific  heat  of  air  for  a  constant  pressure  is  .2374, 
therefore  the  amount  of  heat  required  for  an  increase  of 
temperature  of  1°  F.  is  1,832  X  .2374  =  435  B.  T.  U., 
nearly.  The  air  is  preheated  by  the  regenerators  to  1,500°  F., 
which  is  an  increase  of  1,468°  F.  over  the  temperature 
assumed  for  calculation.  The  heat  recovered  from  the 
regenerators,  therefore,  amounts  to  1,468  X  435  =  638,580 
B.  T.  U.  for  each  net  ton  of  coal  coked.  According  to 
analyses,  the  gas  at  this  plant  yields  567  B.  T.  U.  per 
cubic  foot,  and  this  amount  of  heat  is  equivalent  to  a 
saving  of  638,580  -f-  567  =  1,126  cubic  feet  of  gas  for  each 
ton  of  coal  coked.  The  saving  in  gas  is  not  the  only  advan¬ 
tage  derived  from  the  system,  for  time  is  saved  in  the 


24 


BY-PRODUCT  COKING 


§71 


coking,  as  the  heat  from  the  regenerators  hastens  the  distil¬ 
lation  of  a  fresh  charge  of  coal,  where  cold  air  would  retard 
the  operation  for  a  time  until  the  ovens  had  recovered  their 
heat. 

21.  Control  of  the  Oven  Heat. — The  combustion  in 
the  oven  is  observed  through  peep  holes  left  for  that  pur¬ 
pose  in  the  end  of  the  oven  walls  between  the  buckstaves, 
and  placed  so  that  they  command  a  view  of  the  combus¬ 
tion  chambers.  If  the  gas  pipe  leading  into  the  com¬ 
bustion  chamber  is  clogged,  this  is  easily  detected  here,  as 
then  the  combustion  chamber  is  not  filled  with  gas.  It  is 
also  advantageous  to  inspect  the  combustion  chambers  on  the 
side  on  which  the  gas  is  not  entering,  as  the  amount  of  gas 
coming  down  through  the  vertical  flues  between  the  retorts 
can  then  be  noted.  A  battery  of  ovens  'may  be  said  to  be 
burning  properly  when  the  waste  gases  descending  into  the 
regenerators  show  a  slight  mistiness,  though  not  enough 
to  obscure  the  view  of  the  whole  length  of  the  combustion 
chamber.  This  indicates  that  the  combustion  is  practically 
complete  in  the  oven  flues  and  passages  and  that  the  esca¬ 
ping  gases  are  incombustible  and,  therefore,  will  give  up 
only  their  waste  heat  to  the  checker  brick,  without  any  of 
the  gas  burning  there  and  thus  producing  a  temperature 
high  enough  to  damage  the  reversing  dampers  and  stack 
flue.  An  excess  of  gas  in  the  flue  leading  to  the  regenera¬ 
tor  indicates  that  the  combustion  in  the  oven  flues  is  not 
complete  enough  to  develop  the  full  temperature  about  the 
retort  where  it  is  most  desired,  but  that  the  highest  heat 
will  be  reached  in  the  regenerators,  to  their  possible  detri¬ 
ment  and  certainly  to  the  disadvantage  of  the  coking  proc¬ 
ess.  Such  a  condition  indicates  either  too  much  gas 
pressure  or  not  enough  air.  The  air  chamber  on  the  air¬ 
heating  side,  which  can  be  closely  observed,  as  there  is 
nothing  to  obscure  the  view,  should  show  an  even  heat  the 
whole  of  its  length,  without  the  alternate  dark  and  light 
rings,  which  mark  uneven  heating.  The  gases  issiiing  from 
the  smoke  stack  should  show,  at  most,  a  white  vapor  due  to 


§71 


BY-PRODUCT  COKING 


25 


condensed  moisture.  If  any  black  smoke  appears,  it  is  a 
sign  that  the  gas  is  not  being  properly  burned. 

By  referring  to  Fig.  6  and  assuming  that  combustion  is 
taking  place  in  the  combustion  chamber  n ,  the  flame  from 
the  burning  gas  will  decrease  from  the  door  to  the  parti¬ 
tion  p .  It  will  be  evident  that  the  flame  in  the  other  half  of 
the  oven  will  first  pass  down  into  the  chamber  n'  through 
the  flues  nearest  the  partition  p  and  decrease  gradually 
to  the  door,  thus  the  flues  nearest  the  door  will  receive  the 
smallest  quantity  of  heat.  This  will  make  considerable  dif¬ 
ference  in  the  quality  of  coke  at  the  door  ends  if  the  heat 
is  not  frequently  reversed,  so  as  to  alternately  heat  the 
flues  near  the  oven  doors.  This  difference  of  heat  is  of 
small  moment  in  the  33-foot  oven,  but  precludes  any  possi¬ 
bility  of  increasing  its  length  beyond  that  figure. 


UNDERFIRED  BY-PRODUCT  RETORT  OVENS 


OTTO-HILGENSTOCK  RETORT  OVENS 

22.  In  the  Otto-Hoffman  ovens  thus  far  described,  the 
gas  enters  and  is  ignited  alternately  at  each  end  of  the  oven, 
With  the  vertical  flues,  it  is  difficult  to  distribute  the  heat 
uniformly  by  this  method  of  firing;  hence  to  economize  in 
fuel  and  to  heat  both  ends  of  the  oven  as  nearly  uniformly 
as  possible  through  the  entire  coking  operation,  Messrs. 
Otto  and  Hilgenstock  have  devised  a  method  of  underfiring 
the  ovens.  The  gas  enters  the  combustion  chamber  from 
below  and  from  several  points  instead  of  through  a  single 
opening  at  each  end.  The  Otto-Hilgenstock  oven  shown 
in  cross-section,  Fig.  11,  has  come  into  prominence  abroad, 
and  although  the  coke  oven  entire  has  not  been  introduced  in 
America,  the  principle  of  underfiring  has  been  adopted  in 
one  instance  at  least.  The  section  a  at  the  right  of  the 
line  A  B,  Fig.  11,  is  taken  through  the  retort,  and  the  sec¬ 
tion  b  at  the  left  of  the  line  A  B  is  taken  through  the  retort 
walls  so  as  to  show  the  flue  construction.  The  combustion 


§71 


BY-PRODUCT  COKING 


27 


chambers  c  beneath  the  vertical  flues  are  separated  by  parti¬ 
tions  d  in  such  a  manner  that  a  central  chamber  e  is  formed 
that  has  ports  leading  to  the  chambers  /  directly  beneath  the 
ovens.  The  vertical  flues  g  and  h  are  separated  by  a  central 
partition  i. 

The  gas  for  heating  the  ovens  is  delivered  to  each  oven 
by  branch  pipes  j  connected  with  the  gas  main  k.  Each 
branch  pipe  j  has  connected  to  it  ten  vertical  pipes  l  of  such 
a  diameter  that  they  will  stand  in  the  burner  holes  m  with¬ 
out  filling  the  latter.  Each  vertical  pipe  is  supplied  with  a 
valve  n  to  regulate  the  flow  of  gas  through  it. 

The  air  for  combustion  is  admitted  at  the  bottom  of  the 
holes  m  and  passing  upwards  comes  in  contact  with  the 
gas  issuing  from  the  pipe  l.  This  arrangement  virtually 
forms  a  Bunsen  burner,  the  flame  from  which  rises  up 
through  the  flues  g. 

The  gas,  when  burning,  is  drawn  toward  the  partition  i 
and,  being  baffled,  passes  down  into  the  chamber  e.  Assu¬ 
ming  that  the  flame  of  combustion  is  now  extinct,  the  waste 
gases  pass  into  /,  then  through  the  flue  o  into  the  waste-gas 
main  p,  and  out  to  the  stack.  As  there  are  no  regenerators, 
the  waste  heat  from  the  ovens  cannot  be  utilized  for  pre¬ 
heating  the  air  for  combustion  but  may  be  utilized  under 
steam  boilers. 

The  distribution  of  heat  is  said  to  be  more  uniform  with 
this  system  than  with  end  firing.  The  remainder  of  the 
oven  does  not  differ  much  in  arrangement  and  construction 
from  the  Otto-Hoffman  oven.  The  method  of  charging  by 
the  larries  q ,  of  raising  the  oven  doors  by  winches  r,  and 
the  high  off-take  s  with  its  gas  main  t  have  given  place  in 
the  United  States  to  more  improved  methods  and  appliances. 


SCHNIEWIND,  OR  UNITED-OTTO,  BY-PRODUCT  COKE  OVEN 

23.  The  improved  heat  distribution  in  the  Otto-Hilgen- 
stock  ovens  induced  Doctor  Schniewind  to  combine  the 
underfiring  system  with  the  regenerative  system.  He 
further  simplified  the  oven  construction  by  substituting  a 


28 


BY-PRODUCT  COKING 


§71 


steel  substructure  for  the  masonry  foundation.  It  was 
claimed  by  the  opponents  of  the  regenerative  system  of 
heating  the  air  that  the  heat  absorbed  expanded  the  masonry 
and  caused  it  and  the  retorts  to  crack.  In  order  to  avoid 
this,  the  regenerators  are,  in  some  instances,  placed  outside 
of  the  oven  walls,  and  in  the  Schniewind  type  of  oven 
the  regenerators,  although  directly  under  the  ovens,  are 
separated  from  the  oven  substructure. 

24.  Fig.  12  (a)  and  (b)  shows  longitudinal  sections  of 
the  Scliniewind  oven  and  Fig.  12  (r)  and  ( d )  cross- 
sections  through  a  series  of  ovens  in  a  block  taken  on  the 
lines  A  B  and  CD  in  (a)  and  (b) ,  respectively.  The  foun¬ 
dations  a  that  support  the  substructure  are  of  concrete;  the 
posts  b ,  girders  c,  and  floorbeams  d  are  of  steel.  The 
subfloor  e  is  constructed  of  refractory  material. 

Fig.  12  ( b )  is  a  longitudinal  section  through  a  retort  on 
the  line  CD  of  (d).  If  the  air  enters  through  the  regener¬ 
ator  /,  it  passes  up  through  the  flue  g  into  the  air  chamber  h 
situated  directly  under  the  retort  o.  The  air  now  passes 
from  h  into  the  air  chambers  below  and  then  through  the 
holes  i  into  the  combustion  chambers  j  shown  in  the  section 
at  the  left  in  Fig.  12  (d) .  Through  the  floor*?,  Fig.  12  («), 
under  the  combustion  chambers,  there  are  ten  gas  pipes  k,  k ' 
- — five  connected  to  each  gas  main  /,  l’ .  The  flow  of  gas 
through  each  pipe  k ,  k'  is  controlled  by  a  separate  valve, 
which  admits  of  independent  regulation.  Above  each  com¬ 
bustion  chamber,  there  are  four  vertical  flues  terminating  at 
the  top  in  a  horizontal  flue  m  through  which  the  hot  gases 
pass  to  the  vertical  flues  on  the  left-hand  side  of  the  par¬ 
tition  n.  The  course  of  the  hot  gases  is  then  through  the 
holes  V  into  the  chamber  h',  through  a  flue  g',  to  the  gen¬ 
erator  f  and  thence  to  the  stack. 

Fig.  12  (*:)  is  a  cross-section  through  several  ovens  on  the 
lines  A  B  of  ( a )  and  (b)  taken  through  the  regenerator 
flues  g ,  and  the  regenerators  /.  The  flues  h  are  under  the 
retorts  o ,  the  hot  air  passing  from  h  into  the  combustion 
chambers/,  where  it. meets  the  fuel  gas  entering  through  the 


82417 


§71 


BY-PRODUCT  COKING 


29 


pipes  k ,  Fig.  12  {a).  The  flames  rise  up  the  vertical  flues 
to  the  horizontal  flue  m,  and  travel  across  the  oven  to  the 
other  end  of  the  retort  and  down  the  descending  flues. 

Fig.  12  ( d )  shows,  at  the  left,  a  section  on  the  line  CD  of 
Fig.  12  ( b )  and  at  the  right  an  elevation  of  the  oven  fronts. 
The  section  at  the  left  is  taken  through  the  gas  entrances 
and  shows  that  the  flame  passes  directly  from  the  combustion 
chambers  j  up  flues  between  two  retorts  as  o,  o ,  thus 
imparting  heat  to  each.  The  elevation  shows  the  doors  q 
and  the  buckstaves  r;  the  latter  have  grooves  in  which  the 
doors  slide  when  raised  or  lowered.  The  holes  s  in  the 
doors  are  for  leveling  the  coal  when  charged  into  the 
retorts.  This  elevation  is  at  the  end  of  a  block  of  ovens 
and  shows  the  brick  end  walls  l,  and  the  steel  posts  b  support¬ 
ing  the  transverse  steel  stringers  c,  which,  in  turn,  support 
the  longitudinal  steel  floorbeams  d. 

At  one  end  of  a  block  of  ovens,  there  is  a  chamber  con¬ 
taining  the  proper  appliances  for  changing  the  flow  of  gas 
through  the  gas  pipes  /,  Fig.  12  (a),  {b),  and  (d) ,  from  one 
end  of  the  ovens  to  the  other,  and  for  reversing  the  air- 
current  through  the  regenerators.  There  are  two  off¬ 
takes  u,  u' ,  Fig.  12  ( b )  and  (d) ,  to  these  retorts,  which  deliver 
the  gas  into  the  gas  mains  v,  v'  connected  with  each  off-take. 
By  this  arrangement,  the  rich  gas  may  be  kept  separate  from 
the  poorer  gas.  The  gas  coming  off  during  the  first  period 
is  treated  for  illuminating  purposes  and  that  coming  off  after 
this  period  is  treated  for  fuel  purposes.  The  flow  of  gas 
from  the  oven  is  regulated  and  directed  to  the  proper  gas 
main  by  a  system  of  valves. 

There  are  six  charging  holes  w  in  the  top  of  these  ovens, 
besides  the  two  gas  off-takes.  This  number  of  openings  is 
made  possible  by  the  length  of  the  oven,  which  is  43  feet. 
End-fired  ovens  could  not  be  depended  on  for  first-class  coke 
if  constructed  of  this  length,  although  there  would  be 
economy  in  the  additional  length  since  fixed  charges  would 
be  reduced  by  the  increased  output. 


151  24 


§71 


BY-PRODUCT  COKING 


31 


HORIZONTAE-FEUE  BY-PRODUCT  COKE  OVENS 


SEMET-SOLVAY  COKE  OVENS 

25.  The  general  appearance  of  a  Semet-Solvay  by¬ 
product  oven  plant  is  shown  in  Figs.  13  and  14,  which  show 
the  plant  at  Dunbar,  Pennsylvania.  Fig.  13  shows  the  wharf 
side  and  Fig.  14  the  pusher  side.  The  coal  to  be  coked  is 
stored  in  the  oven  bin  a ,  Fig.  13,  and  is  drawn  off  in  larries 
when  needed  for  oven  charging.  The  arrangements  that 
have  previously  been  described  for  by-product  oven  charging 
may  be  applied  to  these  ovens.  The  coke  is  pushed  from 
the  retort  oven,  by  machine,  on  to  the  pan  b,  where  it  is 
quenched  with  water,  as  shown.  The  pan  in  this  case  is 
mounted  on  wheels  and  as  the  ovens  are  near  the  blast 
furnace  where  the  coke  is  used,  the  pan  is  taken  to  the 
furnace-coke  stock  pile  and  there  dumped,  after  which  it  is 
brought  back  to  receive  the  coke  from  the  next  oven.  There 
are  two  batteries  c  and  d  of  twenty-five  ovens  each  at  this 
plant,  separated  by  a  space  in  which  there  are  four  tubular 
boilers  e  that  utilize  the  heat  from  the  waste  gases  before  they 
pass  into  the  stack  /.  The  water  needed  for  cooling  the 
by-product  apparatus^  and  for  watering  the  coke  is  impounded 
and  pumped  to  the  water  tower  from  which  it  is  drawn  as 
needed. 

The  front  of  the  same  oven  plant  is  shown  in  Fig.  14. 
The  coke  pusher  i  is  different,  in  detail,  from  those  already 
described,  but  in  a  general  way  it  consists  of  a  long  steel 
beam  supplied  with  a  rack  with  a  ram  j  at  one  end.  The 
rack  is  moved  forwards  by  a  pinion  driven  by  a  steam 
engine  or  an  electric  motor,  and  this  movement  pushes  the 
coke  from  the  oven.  The  sheet-iron  oven  doors  k  swing  on 
hinges  and  are  merely  veils  to  prevent  the  radiation  of  heat 
from  the  oven  door  proper.  The  gas  main  l  is  connected 
with  an  off-take  m  at  the  top  of  each  oven,  and  is  also  con¬ 
nected  with  a  pipe  n  through  which  the  gas  passes  to  the 
by-product  apparatus. 


33 


(c)  Sect/on  G-G 


34 


BY-PRODUCT  COKING 


§71 


26.  Semet-Solvay  Retort. — The  retort  chamber  of  the 
Semet-Solvay  oven,  Fig.  15  (a)  and  (b) ,  is  rectangular; 
although  sometimes,  in  order  to  assist  the  coke  pushing,  the 
rear  end  is  made  about  1  inch  wider  than  the  front  end. 
The  dimensions  of  the  retorts  have  been  frequently  varied 
so  that  the  length  ranges  from  26  to  32  feet,  the  width  from 
16  to  20  inches,  and  the  height  from  5  feet  6  inches  to  7  feet. 
The  capacity  of  an  oven  having  the  smaller  dimensions 
given  will  be  4  tons  of  coal;  while  the  capacity  of  an  oven 
constructed  on  the  larger  dimensions  will  be  6  tons  of  coal. 
There  should  be  left  a  space  of  from  8  to  12  inches  between 
the  top  of  the  coal  and  the  retort  arch  in  order  that  the  gases 
may  find  egress  through  the  off-take  a,  Fig.  15  (a),  and  to 
permit  the  swelling  that  occurs  before  the  coal  is  coked. 

The  sides  of  the  coking  chamber  are  constructed  of  rows 
of  hollow  fireclay  tile  b.  These  tile,  called  recuperator  flue 
brick  by  some  firebrick  makers,  are,  as  shown  at  Fig.  15  (d) , 
made  in  one  piece  with  a  bell  end  a  and  spigot  end  b,  so  as 
to  fit  into  each  other  at  the  ends;  they  are  grooved  and 
tongued  so  that  they  will  form  gas-tight  rabbeted  joints  with 
brick  placed  above  and  below.  In  order  to  fix  the  joints 
nicely,  it  may  be  necessary  to  smooth  them  by  hand  or  by 
machine  and  use  a  thin  fireclay  mortar  in  addition.  The 
firebrick  arch  c ,  Fig.  15  (a)  and  ( b ),  above  the  retort  rests  on 
the  flue  bricks  b,  and  it  is  about  all  the  weight  the  latter  have 
to  sustain.  In  order  to  provide  for  the  expansion  and  con¬ 
traction  of  the  hollow  tile  b  and  the  arch  c,  a  space  d  above  c 
is  filled  with  sand.  The  next  arch  e  above  the  sand  is  of  fire¬ 
clay  brick.  Above  the  arch  e>  there  is  a  red-brick  arch  /.  The 
weight  of  the  arch  e  and  the  load  it  carries  come  on  the  refrac¬ 
tory  walls  g,  between  two  ovens  and  not  on  the  tile  b. 

In  the  top  of  the  oven  there  are  four  openings,  the  off¬ 
take  a  at  the  front  end,  and  three  trunnel  heads  h.  The 
coal  is  charged  through  the  trunnel  heads,  for  which  reason 
they  are  fitted  with  iron  covers  and  clamps  i,  Fig.  15  (b). 
After  closing  and  clamping  these  covers,  they  are  luted  with 
clay  to  seal  them  air-tight.  The  oven  floor  j  is  made  of  fire¬ 
clay  tile,  and  separates  the  retort  from  the  hearth  flue  k, 


§71 


BY-PRODUCT  COKING 


35 


which  extends  the  entire  length  of  each  oven.  Below  the 
hearth  flue,  there  is  an  air  flue  /  that  extends  the  entire 
length  of  the  battery  of  ovens.  The  oven  foundation  con¬ 
tains  four  masonry  arches  m  and  n  that  extend  from  one 
end  of  the  battery  to  the  other  and  which  are  utilized  to  pre¬ 
heat  the  air  used  for  the  combustion  of  the  gases  that 
heat  the  retorts.  The  outside  air  has  access  to  the  two  inner 
arches  n  and  must  pass  through  them  into  the  outer  arches  m 
before  it  can  reach  the  air  flue  /  and  the  combustion  cham¬ 
bers.  The  air  passages  leading  from  the  air  flue  to  the  com¬ 
bustion  chambers  are  in  the  walls g  between  each  two  ovens, 
and  reach  the  combustion  chamber  by  offsets  o ,  Fig.  15  (b) . 

27.  Oven  Doors. — The  ends  of  the  retort  have  cast-iron 
door  frames  p  that  fit  snugly  to  the  ends  of  the  flue  bricks  b. 
These  frames  are  held  in  place  by  the  buckstaves  q  and  the 
expansion  bolts  and  nuts  r ,  which  govern  the  longitudinal 
expansion  of  the  masonry.  The  buckstaves  are  not  screwed 
up  tight  to  the  walls  until  the  oven  masonry  has  become 
thoroughly  dried  out  and  heated. 

At  the  front  and  back  ends  of  the  retort  are  doors  con¬ 
structed  of  firebrick  and  cast  iron  that  are  raised  and  lowered 
by  jacks.  In  some  cases  they  are  raised  by  hydraulic 
arrangements  situated  between  the  two  batteries  and  con¬ 
nected  to  the  jacks  that  raise  the  doors.  The  front  door  of 
each  oven  has  a  sheet-iron  screen  that  swings  on  hinges, 
making  a  sort  of  double  door  at  this  end.  The  doors  are 
made  air-tight  by  luting  them  with  clay  and  wedging  them 
against  the  retort-door  frame.  The  hole  s,  Fig.  15  ( b ), 
shown  in  the  door  is  for  the  purpose  of  leveling  the  charge; 
while  through  the  hole  /,  the  condition  of  the  heat  in  the 
hearth  flue  k  is  examined. 

28.  Combustion  Chambers. — The  hollow  tile  b, 
Fig.  15  (d),  forming  the  sides  of  the  retort  of  a  Semet- 
Solvay  oven  are  arranged  so  as  to  form  three  flues  u , u' ,  u" , 
as  shown  in  Fig.  15  (c) .  The  gas  is  admitted  to  the  top 
and  middle  flues  by  2-inch  gas  pipes  v,  v'  provided  with 
suitable  valves  to  regulate  its  flow.  At  the  same  ends  of 


36 


BY-PRODUCT  COKING 


71 


the  flues,  air  is  admitted  for  combustion,  the  air  coming-  from 
the  air  flue  l  through  flues  w  shown  by  the  dotted  lines  in 
Fig.  15  (c),  to  the  points  o  shown  in  Fig.  15  {b) .  The 
burning  gases  pass  from  the  front  to  the  rear  of  the  top 
combustion  chamber  u,  Fig.  15  (c),  and  thence  into  the  flue  u' 
through  the  opening  x  joining  the  two,  as  shown  in  the 
left-hand  section  DD  of  Fig.  15  (b) .  The  flame  passes 
through  this  opening  and  with  the  additional  flame 
produced  by  burning  the  gas  entering  at  v',  Fig.  15  (c), 
moves  to  the  front  of  the  middle  combustion  chamber  u'  and 
through  openings  x'  in  the  tiles,  as  shown  in  section  F Fy 
Fig.  15  (b) ,  into  the  lower  combustion  chamber  u" .  From 
this  point,  the  flame  passes  to  the  rear  and  down  an  open¬ 
ing  x"  connecting  with  the  hearth  flue  k,  thence  to  the  stack 
flue  y.  The  waste  gas,  after  leaving  the  boilers,  enters  the 
stack  with  sufficient  heat  to  cause  a  draft  that  will  draw  air 
into  all  the  combustion  flues  of  the  ovens  without  the  assist¬ 
ance  of  an  exhaust  fan. 

29.  Partition  Walls. — Between  the  flues  of  two  adja¬ 
cent  ovens,  solid  18-inch  walls  gy  Fig.  15  (b) ,  of  firebrick  are 
constructed.  The  lining  is  thus  practically  independent  of 
the  walls  separating  the  ovens.  There  being  two  sets  of 
flue  bricks  and  two  sets  of  gas  burners  between  each  two 
retorts,  it  is  evident  that  without  thick  walls  separating  the 
retorts  there  would  be  a  loss  of  heat,  particularly  when  there 
are  no  regenerators,  as  in  this  type  of  oven.  In  the  Semet- 
Solvay  ovens,  the  combustion  of  gases  heats  the  sides  and 
floor  of  the  retort  bright  red  and,  by  transmitting  this  heat, 
cokes  the  coal  rapidly  and  completely  in  24  hours.  Owing 
to  the  thinness  of  the  flue  walls,  the  heat  passes  through 
them  readily  to  the  coal  and  to  the  walls  between  the  ovens. 
Toward  the  end  of  the  coking  process,  the  coke  becomes 
hotter  than  the  gas  and  gives  out  heat  that  is  absorbed  by 
the  division  walls.  After  the  ovens  have  been  drawn  and 
recharged,  the  division  walls  immediately  deliver  up  a  part 
of  their  heat,  thus  aiding  the  gas  to  supply  quickly  to  the 
coal  the  heat  required  to  start  the  operation  of  coking. 


§71 


BY-PRODUCT  COKING 


37 


30.  Regulation  of  Combustion  in  tlie  Retort  Flues. 
The  horizontal  flues  in  the  retort  tiles  have  been  termed 
combustion  chambers  because  combustion  of  gas  occurs 
in  them.  To  regulate  the  flow  of  gas,  the  gas  supply 
pipes  v,  v’  are  provided  with  valves;  and  to  regulate  the 
flow  of  air  for  combustion,  the  air  flues  l  are  supplied  with 
dampers  at  z ,  which  are  worked  from  outside  the  oven  by  an 
iron  rod.  When  the  oven  gas  and  air  are  properly  adjusted, 
flames  should  show  in  the  combustion  chambers  but  not  in 
the  hearth  flue.'  This  condition  can  be  ascertained  by  exam¬ 
ining  the  lower  flue  and  the  hearth  flue  through  peep  holes 
left  in  front  and  back  walls  for  the  purpose.  The  heat  con¬ 
dition  in  the  upper  flues  u  cannot  well  be  established,  owing 
to  their  being  filled  with  flames,  unless  the  gas  is  shut  off, 
and  this  course  is  recommended  to  be  pursued  twice  in 
24  hours.  If  carbon  has  been  deposited  on  the  walls,  too 
much  gas  and  not  enough  air  for  combustion  has  been 
admitted,  and  the  supply  of  gas  and  air  should  then  be 
properly  regulated.  This  carbon  must  be  burned  off,  as  it 
prevents  heat  from  radiating  properly  through  the  walls. 
The  second  flues  u'  should  next  be  treated  in  a  similar  man¬ 
ner,  and  the  air  and  gas  regulated.  The  heat  at  the  junction 
of  the  first  and  second  flues  should  not  be  so  great  as  to  fuse 
the  tile. 

As  a  rule,  ovens  having  hot  bottoms  and  somewhat  cooler 
tops  make  good  coke  and  furnish  a  better  yield  of  by-products 
than  ovens  having  cooler  bottoms.  It  is  stated  that  ovens 
with  intensely  hot  tops  tend  to  dissociate  the  elements  form¬ 
ing  the  ammonia  and  to  transform  tar  in  the  gas  into  soot, 
in  which  form  it  causes  trouble  by  clogging  the  gas  mains. 


COKE  FROM  RETORT  OVENS 
31.  Owing  to  the  fact  that  retorts  are  long  and  narrow 
and  that  the  heat  for  the  coking  operation  is  supplied  from 
the  side  walls,  coking  takes  place  from  each  side  toward  the 
center  so  that  the  coke  has  the  appearance  shown  in  Fig.  16. 
This  figure  is  a  vertical  section  through  a  retort  showing  the 


38 


BY-PRODUCT  COKING 


§71 


air  chamber  c ,  the  passages  o  through  which  the  preheated 
air  enters  the  combustion  chamber  n,  the  vertical  flues  r, 
and  the  horizontal  flues  s,  and  trunnel-head  section  /.  The 
coke  has  a  very  compact  texture  and  is  quite  hard.  It 
is  used  for  blast-furnace  or  foundry  smelting;  and  although 
it  was  thought  by  some  to  be  too  hard  and  dense  to  permit 
gases  to  permeate  it  or  to  permit  combustion,  actual  tests  do 

not  indicate  that  it  is 
inferior  as  a  metallur¬ 
gical  coke  to  beehive 
coke.  It  is  stated  that 
85  per  cent,  of  the 
coke  made  in  beehive 
ovens  will  be  compact 
and  dense  and  15  per 
cent,  will  be  spongy; 
also  that  81  per  cent, 
of  the  coke  from  by¬ 
product  ovens  will  be 
compact  and  dense 
and  19  per  cent,  will 
be  spongy.  By-prod¬ 
uct  retort  coke  is  in 
every  way  superior  as 
a  domestic  fuel  to 
gas-house  coke,  as 
the  latter  is  spongy 
and  is  consumed 
quickly. 

Fig.  16  32.  Preparing 

Coke  for  the  Domestic  Market.— In  order  to  prepare  coke 
for  domestic  use,  it  is  crushed  in  toothed  crushers  and  then 
sized  in  revolving  screens  that  have  different-sized  openings 
in  different  sections  of  the  screen.  The  sizes  produced  in 
screening  are  the  following: 

Furnace  .  .  .  Over  2i-inch  mesh 

Egg  ....  Over  2i-inch  mesh,  through  2a-inch  mesh 


§71 


BY-PRODUCT  COKING 


39 


Stove  ....  Over  2-inch  mesh,  through  21-inch  mesh 

Nut . Over  i-inch  mesh,  through  2-inch  mesh 

Breeze  .  .  .  Through  i-inch  mesh 

From  the  screens,  the  several  sizes  pass  to  loading  bins; 
and  in  discharging  from  these  bins,  the  coke  passes  over 
apron  screens  that  remove  any  breeze  or  dirt  that  has 
accumulated  after  passing  through  the  large  screen.  Cer¬ 
tain  sizes,  and  particularly  what  is  called  nut ,  is  packed  in 
20-pound  bags  for  retail  trade.  There  is  a  good  demand  for 
this  size  of  coke  in  cities  where  anthracite  is  high  priced. 
An  extensive  trade  has  also  been  built  up  in  egg-size  coke 
for  heaters  and  furnaces,  as  this  size  is  larger  and  will  burn 
longer  than  nut.  _ 


GAS  FOR  HEATING  RETORTS 
33.  By-Product  Gas. — The  first  gases  that  are  distilled 
from  the  coal  in  the  retorts  are  rich  in  illuminants,  while 
those  given  off  during  the  latter  half  of  the  coking  operation 
are  quite  poor,  in  comparison;  they  are,  however,  suitable 
for  heating  coke  ovens  and  for  other  fuel  purposes.  A  coal 
having  28  per  cent,  of  volatile  matter  should  yield  at  least 
10,000  cubic  feet  of  gas  per  ton.  During  the  first  period  of 
coking,  lasting  9  hours,  the  marsh  gas,  which  is  the  chief 
hydrocarbon  in  illuminating  gas,  diminishes,  while  the  hydro¬ 
gen  increases.  The  heating  power  of  the  gas  also  diminishes 
but  not  to  such  an  extent  as  to  cause  the  retorts  to  get 
cold.  Prof.  H.  O.  Hoffman,  who  made  experiments  with 
coke-oven  gas,  found  that  the  calorific  power  of  the  gas  per 
cubic  foot  dropped  in  9  hours  from  775  to  685  B.  T.  U.;  the 
specific  gravity  from  .55  to  .49,  and  the  candlepower  from 
18  to  13j.  Further,  he  found  that  during  the  second  period, 
from  the  ninth  to  the  twenty-second  hour,  the  amounts  of 
gas  given  off  during  equal  periods  were  almost  constant  and 
that  during  this  period  the  calorific  power,  specific  gravity, 
and  candlepower  were  also  almost  constant.  He  found,  also, 
that  after  the  second  period,  the  calorific  value  of  the  gas 
declined,  as  well  as  its  specific  gravity  and  candlepower;  the 
quantity  of  gas  also  rapidly  decreased.  Experimenters  differ 


40 


BY-PRODUCT  COKING 


§71 


in  regard  to  the  calorific  value  of  retort-oven  gas,  which  is 
no  more  than  natural,  owing  to  the  different  kinds  of  coal 
used  in  the  experiments;  but  experimenters  nearly  all  agree 
that  it  requires  about  50  per  cent,  of  the  total  gas  evolved  to 
coke  the  coal.  Assuming,  then,  that  the  gas  after  the  first 
period  contains  450  htekf  units  and  amounts  to  5,000  cubic 
feet  for  every  ton  of  coal  coked,  about  2,250,000  heat  units 
are  required  to  coke  1  ton  of  coal. 

34.  Producer  Gas. — In  some  cases,  the  coke-oven  gas 
is  used  entirely  for  illuminating  purposes,  and  producer 
gas  is  substituted  for  it  to  heat  the  retorts.  One  ton  of 
bituminous  coal  will  furnish  130,000  cubic  feei  of  producer 
gas,  having  a  calorific  power  of  150  heat  units  per  cubic  foot. 
About  34.6  per  cent,  of  producer  gas  is  combustible  while 
65.4  per  cent,  is  incombustible,  which  accounts  for  its  low 
calorific  power,  and  makes  it  necessary  to  have  the  oven 
flues  and  regenerators  of  larger  size  if  this  gas  is  to  be  used 
for  heating  the  retorts.  _ 


BY-PRODUCTS  FROM  RETORT  OVENS 

35.  Principal  Products. — The  two  principal  products 

derived  from  coking  coal  in  retort  ovens  are  coke  and  gases. 
The  former  has  been  described.  From  the  gases,  other 
by-products,  such  as  tar  and  ammonia,  are  obtained;  and 
from  the  tar,  still  other  products  are  obtained  by  the  manu¬ 
facturing  chemists.  _ 

BY-PRODUCT  OVEN  GAS 

36.  The  gas  from  retort  ovens  is  practically  the  same 
as  is  obtained  in  a  municipal  gasworks  using  the  same 
quality  of  coal.  This  gas  is  valued  according  to  its  illumi¬ 
nating  power  and  heating  capacity. 

37.  Candlepower  of  Gas.— The  illuminating  power  of 
gas  is  reckoned  in  candlepower,  a  rather  arbitrary  standard 
based  on  the  light  that  a  spermaceti  candle  will  emit  when 
burning  at  the  rate  of  2  grains  of  sperm  per  minute,  or  120 
grains  per  hour.  This  standard  is  not  entirely  satisfactory, 


§71 


BY-PRODUCT  COKING 


41 


as  it  is  claimed  that  one  candle  in  'burning-  will  emit  more 
light  than  another.  It  is,  however,  the  British  Standard 
candlepower.  In  Germany,  the  Hefner  amyl-acetate  spirit 
lamp,  is  taken  as  a  unit  of  light  known  as  the  Hefner  unit , 
which  is  equivalent  to  .91  candlepower.  A  candle-foot  is 
a  measure  of  illumination  and  is  the  intensity  of  a  standard 
candle  at  a  dista7ice  of  1  foot.  In  the  manufacture  of  gas, 
the  term  candle-foot  is,  however,  often  used  to  express 
the  number  of  cubic  feet  of  gas  of  a  known  candlepower 
multiplied  by  that  candlepower;  for  example,  5,000.  cubic  feet 
of  gas  having  a  candlepower  of  18  is  5,000  X  18  =  90,000 
candle  feet. 

38.  Calorific  Power  of  Gas. — The  calorific  value  or 
heat  units  in  a  gas  can  be  calculated  from  an  analysis  of  the 
gas.  Typical  analyses  of  illuminating  and  fuel  gases  are 
given  in  Table  II. 

TABLE  II 


Kind  of  Gas 

Composition 

Calo¬ 

rific 

Value 

B.T.U. 

Unpu¬ 

rified 

Gas 

Can¬ 

CmHn 

C//4 

H, 

CO 

CO ; 

o2 

w2 

per 
cu.  ft. 

dle 

power 

Illuminating 

5-8 

4 1.8 

34-0 

6.5 

3.7 

.3 

7-9 

736 

18.4 

Fuel  .... 

2.5 

32-3 

48.7 

5-9 

2.2 

.4 

8.0 

583 

10.3 

The  quantity  of  gas  evolved  depends  on  the  percentage  of 
volatile  matter  in  the  coal,  and  it  may  be  assumed  that  a 
coal  containing  28  per  cent,  volatile  hydrocarbons  will  yield 
10,000  cubic  feet  of  gas  per  long  ton  of  coal,  and  35  to  40 
per  cent,  of  this  will  be  surplus,  or  more  than  is  needed  for 
coking  purposes.  With  coals  of  a  low  percentage  of  volatile 
matter,  however,  there  is  not  sufficient  surplus  gas  above 
oven  requirements  to  be  of  importance.  The  cost  of  an 
18-candlepower  gas,  unpurified,  as  delivered  by  the  average 
coal  gasworks  varies  between  15  and  40  cents  per  1,000 
cubic  feet,  according  to  the  locality  and  size  of  plant. 


42 


BY-PRODUCT  COKING 


§71 


TAR 

39.  Tar  is  obtained  from  coke-oven  gas  during  the  proc¬ 
ess  of  condensation  by  cooling.  The  amount  varies  approx¬ 
imately  from  2  to  5  per  cent,  of  the  weight  of  the  coal 
carbonized.  A  very  dry  coal  may  fall  short  of,  and  a  rich 
one  exceed,  these  figures.  Coke-oven  tar  usually  contains 
2  to  3  per  cent,  of  ammoniacal  liquor,  which  is  with  difficulty 
removed,  particularly  when  the  tar  is  repumped  through  the 
gas  collecting  mains  to  aid  in  keeping  them  clear  of  pitch. 
Coke-oven  tar  contains  less  free  carbon  than  tar  made  from 
the  same  coal  in  gas-house  retorts.  This  is  possibly  due  to 
its  coming  less  in  contact  with  highly  heated  surfaces  in  the 
oven  retort  than  in  the  gas  retort. 

The  separation  of  the  ammoniacal  liquor  and  the  tar  is 
usually  effected  by  allowing  the  mixture  to  settle  some  time 
in  a  receiving  tank,  the  higher  specific  gravity  of  the  tar 
causing  it  to  sink  to  the  bottom,  while  the  ammoniacal  liquor 
gathers  on  top,  and  can  be  drawn  off.  Steam  coils  in  the 
tank  promote  this  action  by  keeping  the  tar  fluid.  In  some 
works,  a  series  of  several  smaller  tanks  is  used  through 
which  the  tar  flows  in  turn,  the  bottom  tar  from  the  first  tank 
passing  to  the  top  of  the  second  and  so  on,  the  liquor  being 
drawn  off  each  one  separately  to  a  common  receiver.  The 
only  really  effective  way  is  to  heat  the  tar  in  a  still  until 
the  water  passes  off  and  the  first  light  oils  appear,  but  this 
process  is  rather  too  expensive  for  general  use. 

40.  Uses  for  Tar. — In  the  United  States,  tar  is  usually 
disposed  of,  as  recovered,  to  the  manufacturers  of  pitch  and 
saturated  felt,  although  a  few  of  the  by-product  oven  plants 
have  installed  their  own  tar-distilling  or  saturating  plants. 
A  certain  amount  of  tar  is  used  in  its  crude  state  in  the 
manufacture  of  paints  and  varnishes,  waterproofing,  pipe  dip, 
brick  paving,  tar  concrete,  and  allied  products.  Some  tar,  as 
well  as  some  of  the  oils  distilled  from  tar,  is  burned  in  the 
manufacture  of  lampblack.  But  few  of  the  tar  works  carry 
the  distillation  further  than  to  separate  the  light  and  heavy 


§71 


BY-PRODUCT  COKING 


43 


oils  from  the  soft  pitch,  which  is  used  for  roofing  and  paving. 
Hard  pitch ,  as  the  term  is  understood  abroad,  is  not  usually 
made  in  the  United  -States  and  is  in  small  demand  here. 
The  tar  chemical  industry,  which  is  so  highly  developed  in 
Germany,  has  made  but  little  progress  in  the  United  States. 

Table  III  shows  the  various  fractions  obtained  in  coal  tar 
distillation,  and  the  temperatures  at  which  they  come  off: 

TABLE  III 


Fractions 

Commercial  Product 

Up  to  338°  F . 

Ammoniacal  liquor,  solvent  naphtha, 

burning  naphtha 

From  338°  to  446°  F. 

Naphthalene,  carbolic  acid 

From  446°  to  518°  F. 

Creosote  oil  for  impregnation,  lubri¬ 

cating  oil 

From  518°  up  .  .  .  . 

Anthracene 

Residue  . 

Pitch 

The  market  price  of  tar  varies  from  3  to  5  cents  per  United 
States  gallon  according  to  locality  and  conditions;  at  times 
it  has  fallen  below  2  cents  per  gallon.  In  some  districts,  tar 
has  been  burned  as  fuel  with  excellent  results.  As  fuel, 
5  pounds  of  tar  may  be  taken  as  equivalent  to  7  pounds  of 
coal,  although  the  theoretical  ratio  is  given  as  10  to  11,  cal¬ 
culated  on  the  chemical  analysis.  The  first  figure  given  is, 
however,  correct  in  practice,  because  of  the  greater  economy 
obtainable  in  using  a  liquid  fuel,  rather  than  a  solid  fuel. 
There  is  a  further  saving  in  labor  in  the  use  of  tar  as  a  fuel. 
The  method  of  burning  is  usually  to  spray  the  tar  in  a  finely 
divided  condition  into  the  furnace  by  means  of  a  steam  or 
air  jet,  specially  constructed  burners  being  used  for  this 
purpose.  _ 


AMMONIA 

41.  Ammonia  is  recovered  from  the  oven  gas  in  the 
form  of  ammoniacal  liquor  during  the  processes  of  cooling 
and  scrubbing.  Some  ammonia  is  also  obtained  from  the 


44 


BY-PRODUCT  COKING 


§71 


distillation  of  tar.  A  part  of  the  water  forming  the  liquor  is 
due  to  the  moisture  in  the  coal,  the  remainder  is  added  in 
the  scrubbing  to  aid  in  the  final  absorption  of  the  ammonia. 
This  liquor  contains  between  1  and  2  per  cent,  of  ammonia, 
principally  in  the  form  of  chloride,  sulphate,  sulphide,  car¬ 
bonate,  and  hydrate.  Of  these,  the  carbonate,  sulphide,  and 
hydrate  are  regarded  as  free  ammonia ,  or  ammonia  that  may 
be  driven  off  by  heat  alone.  The  chloride  and  sulphate  are 
decomposed  by  heat  only  in  the  presence  of  an  excess  of  an 
alkali,  such  as  lime,  sodium  carbonate,  or  sodium  hydrate, 
and  are  therefore  classed  as  fixed  salts.  The  proportion  of 
these  two  forms  of  ammonia  varies  greatly  in  different 
liquors,  being  strongly  influenced  by  the  quality  of  both  the 
coal  coked  and  the  water  used  for  washing  the  gas.  As  the 
free  ammonia  is  much  more  easily  handled  in  distillation,  it 
is  desirable  to  obtain  as  much  of  it  in  this  form  as  possible. 
The  amount  of  ammonia,  NHZ,  recovered  from  ordinary 
coking  coals  may  usually  be  reckoned  as  .25  per  cent,  of  the 
weight  of  the  coal,  or  roughly  speaking,  the  equivalent  of 
1  per  cent,  of  the  weight  of  the  coal  reckoned  as  ammonium 
sulphate.  Assuming  the  strength  of  the  liquor  to  be  1  per 
cent.  NH3 ,  it  is  clear  that  the  weight  of  liquor  produced 
will  be  one-fourth  of  the  weight  of  the  coal  carbonized; 
this  figure  is  of  use  in  approximately  estimating  the  size 
necessary  for  liquor  storage  tanks  and  pumps.  A  stronger 
liquor  than  1  per  cent.,  say  li  or  2  per  cent.,  is  gener¬ 
ally  more  economical  in  concentration,  as  there  is  less 
water  to  heat.  The  concentration  process  consists  in  driving 
off  the  ammonia  from  the  liquor  by  direct  steam  heating  in  a 
closed  vertical  tower  of  cast-iron  sections,  the  escaping  mix¬ 
ture  of  water  and  ammonia  vapors  being  either  condensed 
by  cooling  coils  to  form  crude  strong  liquor  of  15  to  20  per 
cent.  A7/3,  or  passed  through  lead  boxes  containing  dilute 
sulphuric  acid,  if  it  is  desired  to  make  ammonium  sulphate. 
The  ammonium  sulphate  is  dried  and  shipped  in  bulk  or  in 
bags  to  manufacturers  of  chemicals  or  fertilizers,  while  the 
ammonia  water  is  shipped  in  drums  or  tank  cars  to  similar 
industries. 


§71 


BY-PRODUCT  COKING 


45 


BY-PRODUCT  COLLECTING  APPARATUS 

42.  The  nature  of  the  apparatus  used  for  collecting, 
cooling,  and  washing  the  gas  has  no  connection  with  the  type 
of  oven  in  which  the  coal  is  treated.  The  general  principles 
that  govern  the  condensation  of  coal  gas  from  gas-house 
retorts  apply  equally  well  in  the  case  of  coke-oven  gas,  except 
that  the  quantity  of  oven  gas  handled  is  usually  larger. 

43.  Gas-Collecting  Main. — The  gas  is  drawn  from  each 
oven  through  an  off-take,  usually  of  cast  iron,  fitted  over  one 
of  the  openings  in  the  oven  roof  and  kept  tightly  sealed  to  the 
brickwork  with  clay.  This  off-take  is  provided  with  a  valve 
that  admits  the  gas  to  a  single,  large,  gas-collecting  main. 
This  valve  should  be  of  simple  and  strong  construction,  so 
that  it  will  stand  the  hard  usage  it  receives.  It  should  also  be 
provided  with  means  for  freeing  it  of  pitch,  and  for  affording 
access  to  the  off-take  for  the  same  purpose.  The  collecting 
main  may  be  one  of  two  types,  wet  or  dry. 

44.  Wet  Collecting  Gas  Main. — The  wet  type  of  col¬ 
lecting  main  is  usually  adopted  on  the  Semet-Solvay  ovens. 
It  consists  usually  of  a  horizontal  pipe  a , 

Fig.  17,  having  a  baffle  plate  b  that  divides 
it  into  two  compartments  c  and  d  that  are 
sealed  from  one  another  by  water  and  tar. 

The  gas  enters  one  compartment,  asr,  and 
is  drawn  through  the  water  and  beneath  the 
baffle  plate  into  compartment  d by  the  suction 
of  a  blower  called  an  exhauster ,  and  in  this  way  a  preliminary 
cooling  and  condensation  of  tar  is  effected.  This  keeps  the 
gas  in  the  ovens  separate  from  that  in  the  mains,  a  slight 
pressure  being  maintained  on  the  oven  side  of  the  baffle, 
while  the  discharge  side  is  under  a  slight  suction.  The  level 
of  tar  and  liquor  is  maintained  in  the  main  by  an  adjustable 
gate  on  a  separate  overflow  passage  connecting  with  the 
lowest  part  of  the  main,  so  that  only  the  tar  shall  escape. 
The  tar  flows  along  the  gas  main  to  the  condensers  and 
then  through  drains  to  the  tar  well.  The  gas  is  taken  by 

151—25 


Fig.  17 


46 


BY-PRODUCT  COKING 


§71 


an  overhead  connection  from  the  upper  part  of  the  collect¬ 
ing  main. 

45.  Dry  Collecting  Gas  Main. — In  the  dry  gas  main 
system  used  in  the  Otto-Hoffman  ovens,  the  main  may  be 
either  horizontal  or  slightly  inclined,  and  there  is  no  baffle 
plate.  The  exhauster  suction  is  maintained  at  such  a  gauge 
that  all  the  ovens  are  under  a  slight  pressure  and  the  gas 
from  them  passes  directly  into  the  cooling  system. 

In  either  the  wet  or  the  dry  system,  it  is  necessary  to  keep 
the  mains  clear  of  the  pitch  and  tar  that  gathers  in  them  as 
soon  as  the  gas  begins  to  cool  a  little,  by  pumping  a  constant 
stream  of  tar  and  liquor  into  one  end  and  allowing  it  to  escape 
at  the  other.  In  addition  to  this,  openings  are  provided  in 
the  main  through  which  it  is  possible  to  poke  loose  the  accu¬ 
mulation  of  tar  from  the  sides  and  top  of  the  main,  the  stream 
of  tar  and  liquor  passing  along  the  bottom  serving  to  carry 
these  to  the  seal  pot  provided  for  their  removal.  In  a  plant 
having  but  one  battery  of  ovens,  the  seal  pot  should  be  at 
the  nearest  convenient  point  after  the  collecting  main  leaves 
the  battery,  or,  as  is  the  case  in  the  wet  main  system  there 
may  be  traps  on  the  main  through  which  hard  pitch  may  be 
removed.  If  there  are  several  batteries,  it  is  usual  to  bring 
the  mains  together  at  a  central  point,  toward  which  they  all 
slope,  and  collect  the  hard  tar  there  by  means  of  the  circulating 
method  and  by  poking  it  loose  in  the  mains. 

46.  Equalizing  the  Gas  Pressure. — In  order  to  make 
it  possible  to  maintain  a  practically  equal  gas  pressure  on 
all  the  ovens,  the  collecting  main  must  be  of  sufficient  size 
to  act  as  an  equalizing  reservoir  between  the  ovens,  at  the 
same  time  delivering  to  the  gas  main.  Where  several  bat¬ 
teries  are  connected  to  one  system  of  gas  mains,  the  pres¬ 
sure  in  the  individual  collecting  mains  on  each  battery  is 
regulated  by  opening  and  closing  the  valves  between  them 
and  the  main  gas  system.  With  a  single  battery  having  but 
one  main,  the  pressure  may  be  regulated  by  regulating  the 
exhauster.  The  pressure  on  the  ovens  is  due  to  the  fact 
that  the  gas  is  evolved  more  rapidly  than  it  can  escape 


§71 


BY-PRODUCT  COKING 


47 


through  the  openings.  An  exhauster  relieves  this  pressure 
without  going  so  far  as  to  cause  it  to  fall  below  the  atmos¬ 
pheric  pressure.  For  the  best  conditions,  there  should  be  a 
slight  outward  pressure  of  gas  in  the  oven,  as  this  avoids 
the  entrance  of  air  through  cracks  and  the  consequent  dilu¬ 
tion  of  the  oven  gases  and  combustion  of  coke.  Too  great 
a  pressure,  however,  causes  the  gas  to  force  its  way  through 
the  flue  walls  and  burn  there  along  with  the  heating  gas, 
which  not  only  results  in  a  loss  of  the  by-products,  but  also 
probably  in  the  cooling  off  and  choking  of  the  flue  with  car¬ 
bon.  Too  much  gas  is  as  prejudicial  to  high  heats  as  too 
little.  For  these  reasons,  it  is  desirable  to  carry  as  little 
suction  on  the  heating  flues  or  combustion  chambers  as  pos¬ 
sible,  so  as  not  to  facilitate  the  leakage  of  gas  from  the  ovens. 
This  is  one  argument  in  favor  of  the  use  of  a  pressure  blower 
to  supply  the  air  for  combustion,  as  otherwise  the  draft  of  the 
chimney  stack  must  be  depended  on  for  this  service. 


47.  Condensing  House. — The  gas  mains  lead  to  the 
condensing  house,  where  the  gas  is  usually  first  passed 


through  air  coolers,  which  condense  a  large  portion  of  the 
tarry  vapors,  the  remaining  tarry  vapors  being  removed  in 
the  tar  scrubbers.  These  coolers  consist  of  steel-plate  or 
cast-iron  vessels  that  expose  a  large  cooling  surface  to  the 
atmosphere,  and  thus  allow  the  heat  in  the  gas  to  be  dif¬ 
fused.  This  cooling  has  already  begun  in  the  gas  mains 


BY-PRODUCT  COKING 


48 


§71 


themselves,  particularly  when  these  mains  are  carried  above 
ground. 


48.  Air  Coolers. — There  are  a  number  of  kinds  of  air 
coolers,  the  essential  features  of  such  a  cooler  being  a  large 
exposed  surface  in  proportion  to  the  volume  of  gas  passing 

through  the  cooler  and 
proper  drainage  of  the  con¬ 
densed  tar  liquor. 

One  of  the  original  forms 
known  as  a  horizontal  screw 
co7idenser ,  consisted  of  cast- 
iron  pipes  coupled  end  to 
end,  as  shown  in  Fig.  18, 
with  return  bends  placed  in 
a  slightly  inclined  zigzag 
manner,  so  that  gas  passed 
in  at  a  and  out  at  b. 

Fig.  19  shows  a  vertical 
cooler ,  which  consists  of  a 
tall  steel  cylinder  contain¬ 
ing  a  number  of  vertical 
tubes  placed  as  shown  in  the 
cross-section,  so  that  cool 
air  enters  the  tubes  at  the 
bottom  and  passes  out  at  the 
top,  the  amount  being  regu¬ 
lated  by  the  damper  at  the 
top.  The  gas  passes  into 
the  condenser  at  the  top  or 
circulates  around  the  air-cooled  tubes  and  passes  out  at  the 
bottom,  as  shown  by  the  arrows. 

In  the  vertical  pipe  condenser ,  Fig.  20,  the  cooling  pipes 
are  arranged  vertically,  the  lower  ends  of  the  pipes  being 
fitted  into  partitioned  boxes,  or  headers,  of  larger  area  than 
the  pipes,  through  which  water  circulates. 

In  the  annular  conde?iser ,  Fig.  21,  the  vertical  tubes  are  of 
large  size  and  additional  cooling  surfaces  are  supplied  by 


§71 


BY-PRODUCT  COKING 


49 


enclosing  an  internal  air  pipe  in  the  center,  thus  making  the 
space  through  which  the  gas  circulates  annular  in  section. 
Annular  condensers  are  sometimes  made  of  steel  plate 
and  of  large  diameter. 

It  is  clear  that  atmospheric  cooling  is  only  practicable 


Fig.  20 


while  the  gas  is  still  considerably  hotter  than  the  air,  so  that 
the  transmission  of  heat  will  be  comparatively  rapid;  further¬ 
more,  that  this  difference  will  vary  from  the  same  plant  and 


apparatus,  with  the  time  of 
year.  For  this  reason,  the 
air  coolers  are  sometimes 
provided  with  a  water 
spray,  to  aid  the  cooling  in 
warm  weather,  or  they  are 
placed  in  buildings  having 
sides  of  movable  slats,  so 
that  they  may  receive  more 
or  less  wind  as  desired. 
When  both  these  methods 
are  employed,  a  consider¬ 
able  cooling  effect  is 
obtained. 


Fig.  21 


49.  Tubular  Water  Coolers. — When  wet  gas  mains 
are  employed,  air  coolers  other  than  the  gas  mains  them¬ 
selves  are  usually  omitted  and  recourse  is  had  at  once  to  the 
tubular  water  coolers.  These  vary  in  design,  but  are  of 


50 


BY-PRODUCT  COKING 


§71 


the  same  general  type,  consisting  of  a  vessel  of  steel  plate 
through  which  water  tubes  are  led,  the  gas  being  passed 
through  the  vessel  around  the  tubes.  A  type  of  such  a  con¬ 
denser  is  shown  in  Fig.  22.  The  water  spaces  a  and  b  are 
connected  by  a  series  of  tubes  c  through  which  water  circu¬ 
lates.  The  cool  water  enters  at  d  and,  passing  up  through 
the  tubes  that  are  in  contact  with  the  heated  gases,  absorbs 

heat  and  passes  out  at  e. 
The  upper  part  of  this 
condenser  is  open  to  the 
atmosphere.  The  hot  gas 
enters  the  shell  at  /  and  is 
forced  by  the  baffle  plate  g 
and  the  tube  sheets  h  to 
circulate  to  the  top  before 
it  can  find  an  entrance  to 
the  exit  passage  i.  It  is 
thus  cooled  by  the  water 
in  pipes  c,  before  it  finally 
reaches  the  exit  j.  The 
condensed  tar  and  ammo- 
niacal  liquor  trickle  down 
the  tubes  and  sides  of  the 
condenser,  finding  an  out¬ 
let  at  k.  The  efficiency  of 
a  given  amount  of  cooling 
surface  is  thus  consider¬ 
ably  increased  because  the 
gas  just  before  exit  comes 
in  contact  with  the  coolest  surface,  and  the  water  when  leaving 
comes  in  contact  with  the  hottest  surface.  If  the  gas  is  to  be 
divided  into  two  parts  for  commercial  use  and  oven-heating 
purposes,  there  should  be  two  sets  of  mains  and  condensing 
apparatus,  forming  two  distinct  systems,  which  should  be 
practically  the  same  in  construction. 


50.  Effect  of  Water  in  Gas.— Although  the'  gas  is 
spoken  of  as  being  cooled,  this  is  really  a  small  matter 


871 


BY-PRODUCT  COKING 


51 


compared  with  the  cooling  and  condensation  of  the  water 
vapor  contained  in  it,  as  may  be  shown  by  the  following  exam¬ 
ple:  Assume  that  in  the  carbonization  of  2,000  pounds  of  coal, 
10,000  cubic  feet  of  gas  is  given  off.  This  gas,  if  of  a  specific 
gravity  of  .5,  will  weigh  .08073  X  .5  =  .040365  pound 
per  cubic  foot.  The  total  weight  will  be  10,000  X  .040365 
=  403.65  pounds.  If  the  coal,  as  charged  into  the  oven, 
contained  2  per  cent,  of  moisture,  there  being  in  addition 
4  per  cent,  of  chemically  combined  water,  the  weight  of  the 
water  vapor  in  the  resulting  gas  would  be  6  per  cent,  of 
2,000  pounds,  or  120  pounds.  Assume  that  the  gas  is  to 
be  cooled  from  300°  F.  to  70°  F.;  the  heat  that  must  be 
absorbed  in  order  to  effect  this  cooling  may  be  divided  into 
three  portions;  namely,  ( a )  that  in  the  gas  cooled  through 
230°  F.;  ( b )  that  in  the  water  vapor  cooled  through  the 
same  range;  and  (c)  the  latent  heat  in  the  water  vapor 
incident  to  its  change  from  vapor  to  liquid  water.  Assuming 
.45  as  the  specific  heat  of  the  gas  and  .48  as  that  of  the 
water  vapor, 

(a)  403.65  pounds  X  .45  X  230°  =  41,777.8  B.  T.  U. 

(b)  120  pounds  X  .48  X  230°  =  13,248.0  B.  T.  U. 

In  order  to  arrive  at  the  value  of  (c),  the  amount  of  heat 
latent  in  the  condensed  vapor,  first  ascertain  what  portion  of 
the  vapor  is  actually  condensed  at  70°  F.  This  may  be 
found  by  determining  the  amount  of  water  vapor  that  will 
saturate  the  given  weight  of  gas  at  70°  F.  From  Table  IV, 
it  is  found  that  at  70°  F.  100  cubic  feet  of  air  saturated  with 
vapor  will  contain  7.311  pounds  of  air  and  .114  pound  of  water; 
or  as  gas  has  but  .5  the  specific  gravity  of  air,  there  will  be 
3.655  pounds  of  gas  and  .114  pound  of  water,  or  the  water  is 
3.1  per  cent,  of  the  gas.  Hence,  in  403.65  pounds  of  gas, 
there  will  be  403.65  X  .031  =  12.51  pounds  of  water,  which 
subtracted  from  120  pounds  leaves  107.49  pounds  of  water 
actually  condensed,  and  with  the  latent  heat  of  vaporization 
at  965.8  B.  T.  U.  the  value  of  (c)  is 

.  965.8  X  107.49  =  103,813.84  B.  T.  U. 

(a)  +  (b)  +  (c)  =  158,839.64  B.  T.  U., 
of  which  the  gas  contained  only  about  26.3  per  cent,  and 


52 


BY-PRODUCT  COKING 


71 


the  water  73.7  per  cent.  This  disparity  is  due  to  the  latent 
heat  given  off  in  condensing  the  water  vapor,  as  the  pre¬ 
vious  figures  show.  If  instead  of  a  coal  having  but  2  per 
cent,  of  sensible  moisture,  one  having  5  to  8  per  cent.,  as 
frequently  met  with,  is  used,  it  is  clear  that  the  work  thrown 
on  the  cooling  apparatus  will  be  largely  increased. 

51.  Table  IV  gives  the  weight  of  air  and  moisture  at  ordi¬ 
nary  atmospheric  pressure  together  with  the  weight  of  the  mix¬ 
ture  in  100  cubic  feet  of  saturated  air  for  various  temperatures. 

TABLE  IV 


Temperature 
of  the 
Saturated 
Mixture 
Degrees 
Fahrenheit 

Weight  of  ioo  Cubic  Feet 
of  Saturated  Mixture; 
Also  Weight  of 

Water  Vapor  and  Air  in 
the  Mixture 

Pounds 

1 

Temperature 
of  the 
Saturated 
Mixture 
Degrees 
Fahrenheit 

Weight  of  100  Cubic  Feet 
of  Saturated  Mixture; 
Also  Weight  of 

Water  Vapor  and  Air  in 
the  Mixture 

Pounds 

Vapor 

Air 

Saturated 

Mixture 

Vapor 

Air 

Saturated 

Mixture 

32 

.030 

8.023 

8-053 

125 

-554 

5.9OO 

6-454 

35 

•034 

7-970 

8.004 

130 

.630 

5-717 

6-347 

40 

.041 

7.879 

7.920 

135 

.714 

5-524 

6.238 

45 

.049 

7-785 

7.834 

140 

.806 

5.325 

6.131 

50 

•059 

7-693 

7-752 

145 

.909 

5.106 

6.015 

55 

.070 

7-598 

7.668 

150 

1 .022 

4.869 

5.891 

6o 

.082 

7-507 

7.589 

155 

I-I45 

4.619 

5.764 

65 

.097 

7.410 

7-507 

160 

1-333 

4-346 

5-679 

70 

.114 

7-311 

7-425 

165 

1.432 

4-055 

5.487 

75 

•134 

7.208 

7-342 

170 

1.602 

3-739 

5-341 

8o 

.156 

7-iq6 

7.262 

175 

1-774 

3-402 

5.176 

to 

CO 

.182 

6.996 

7.178 

180 

1.970 

3.036 

5.006 

90 

.212 

6.896 

7.108 

185 

2.181 

2.651 

4-832 

95 

•245 

6.764 

7.OO9 

190 

2.411 

2.231 

4.642 

IOO 

.283 

6.641 

6.924 

195 

2.662 

1.781 

4  443 

105 

.325 

6.505 

6.830 

200 

2-933 

1.300 

4-233 

I IO 

•373 

6.368 

6.741 

205 

3-225 

.785 

4.010 

ii5 

.426 

6.224 

6.650 

210 

3-543 

.232 

3-775 

120 

.488 

6.063 

6.551 

212 

3-683 

.000 

3-683 

52.  Cooling  Surface  Required. — The  area  of  cooling 
surface  required  to  sufficiently  cool  1,000  cubic  feet  of  gas 
per  day  under  the  ordinary  conditions  of  manufacture  in  this 


§71 


BY-PRODUCT  COKING 


53 


country  is  assumed  to  be  between  4  and  5  square  feet;  of 
this  .5  to  1.5  square  feet  may  be  air  cooled.  Much  depends 
on  the  difference  in  temperature  between  the  gas  and  the 
cooling  medium.  If  this  difference  is  too  great  and  too 
sudden  cooling  of  the  gas  ensues,  there  will  be  a  loss  in  its 
candlepower;  hence,  when  the  gas  is  used  for  illuminating 
purposes  this  point  must  be  considered.  If  5°  F.  is  the 
maximum  difference  in  temperature  allowed  between  gas 
and  the  cooling  water,  8  square  feet  of  water-cooled  surface 
will  be  necessary  per  1,000  cubic  feet  of  gas  per  day.  If  a 
maximum  difference  of  63°  F.  be  allowed,  as  in  the  recently 
designed  condensers  for  a  London  Gas  Company,  1.71  square 
feet  of  water-cooled  surface  and  1.19  square  feet  of  air¬ 
cooled  surface  may  be  considered  sufficient,  although  for 
atmospheric  condensers  English  practice  prescribes  10  square 
feet  per  1,000  cubic  feet  of  gas.  The  first-mentioned  figures 
are  probably  sufficient  for  all  purposes. 

53.  Temperature  Measurements. — The  proper  con¬ 
trol  of  the  condensation  process  is  entirely  a  matter  of 
regulating  the  temperature  of  the  condensers  and  mains. 
In  order  to  control  these  temperatures,  thermometers  should 
be  placed  at  the  principal  points  where  the  gas  enters  and 
leaves  the  coolers,  and  where  it  leaves  the  condensing  house. 
Ordinary  thermometers  may  be  used;  these  are  generally 
inserted  in  mercury  pockets  at  points  where  the  temperatures 
are  to  be  taken.  They  should  be  read  hourly,  and  the  read¬ 
ings  noted  on  a  printed  form.  A  better  method  is  to  use 
recording  thermometers. 

54.  Pressure  Measurements. — The  gas  pressures  are 
most  easily  observed  by  leading  small  pipes  from  different 
points  in  the  system  to  a  central  gauge  board,  where  all  the 
needed  gauges  are  arranged  in  the  same  order  as  the  con¬ 
densing  apparatus.  Each  gauge  consists  of  a  U-shaped  glass 
tube  filled  with  colored  water,  or  contains  water  on  which  a 
glass  float  indicates  the  height  of  the  water  column.  The 
point  at  which  the  pressure  is  measured  should  be  indicated 
above  each  gauge,  and  the  gauge  board  should  be  sufficiently 


54 


BY-PRODUCT  COKING 


§71 


lighted  so  that  the  gauges  can  be  easily  read  day  or  night. 
Such  a  board  greatly  facilitates  the  control  of  the  process 
and  the  prompt  detection  of  stoppage  in  the  apparatus. 

55.  Exhauster. — The  exhauster,  as  has  been  stated, 
is  used  to  move  the  gas  through  the  mains  to  the  condensing 
house  by  suction  and  to  force  it  through  the  scrubbing  and 
purifying  apparatus  to  the  gas  holder.  Some  form  of  posi¬ 
tive  rotary  blower  similar  to  that  shown  in  Fig.  23,  of  which 
there  are  several  on  the  market,  is  generally  used.  Blowers 
of  the  fan,  or  centrifugal,  type,  though  frequently  used  for 


handling  purified  gas,  are  not  in  favor  for  use  on  foul  gas, 
more  especially  as  the  pressures  frequently  used  in  scrubbing 
apparatus  are  higher  than  those  easily  attainable  by  this 
form  of  fan.  In  installing  exhausters,  the  main  point  to  be 
regarded  is  to  get  them  of  sufficiently  large  capacity  to  easily 
do  the  work,  without  requiring  too  high  a  speed.  They  are 
best  driven  by  steam  engines  coupled  directly  to  the  shafts 
in  preference  to  any  other  form  of  motor,  as  the  speed  can 
then  be  most  easily  regulated.  If  possible,  two  engines  and 
two  exhausters  should  be  installed,  one  being  kept  for  use 
when  the  other  is  being  repaired.  Cocks  and  pipe  connec¬ 
tions  should  be  provided  for  drawing  off  any  accumulation 
of  tar  or  liquor  from  either  side  of  an  exhauster. 


§71 


BY-PRODUCT  COKING 


55 


56. 


TAR  SCRUBBERS 

Pelouze  &  Audouin  Scrubber. — The  best  known 

form  of  tar  scrub¬ 
ber  is  that  of  Messrs. 
Pelouze  &  Audouin. 
The  apparatus, 
Fig-.  24,  consists  of  a 
vessel  a  in  the  middle 
of  which  is  an  annular 
tar  cistern  b.  The 
lower  and  upper  por- 
tions  of  a  are  gas 
chambers.  In  the 
upper  portion  of  a  is 
suspended  the  purify¬ 
ing  apparatus,  which 
consists  of  a  bell  c 
suspended  by  outside 
weights  and  ropes,  as 
shown,  having  double 
cylindrical  sides  con¬ 
taining  small  perfora¬ 
tions.  The  holes  in 
the  outer  wall  are 
larger  than  those  in 
the  inner  wall  and  are 
not  opposite  to  them. 
The  bell  dips  into  a 
tar  seal  at  the  bottom. 
The  gas  enters  the 
lower  part  of  cham¬ 
ber  a  by  the  pipe  d> 
passes  up  into  the 
bell  c ,  which  by  the 
pressure  of  the  gas 
is  lifted  out  of  the 
tar  sufficiently  to  allow  some  gas  to  escape  and  thus  relieve 


56 


BY-PRODUCT  COKING 


71 


the  pressure.  In  this  way,  the  pressure  is  kept  constant  and 
the  flow  of  gas  is  automatically  controlled.  The  gas  now 
passes  through  the  small  perforations  in  the  inner  wall  of  the 
bell  and  strikes  against  the  solid  part  of  the  outer  wall, 
finally  passing  to  the  upper  part  of  a  through  the  larger 
perforations  in  the  outer  wall  and  out  through  the  pipe  e. 
The  friction  of  the  gas  passing  through  the  perforations  and 
against  the  baffling  walls  causes  the  condensation  of  the 
tarry  mist  into  large  drops,  which  do  not  pass  through  the 
holes,  but  fall  into  the  bottom  of  the  vessel  b}  from  which 
the  tar  is  drawn  off  through  suitable  outlets. 

57.  Divesey  Scrubber. — Another  well-known  form  of 
tar  scrubber  is  the  Divesey,  in  which  the  gas  is  admitted  to 
a  closed  vessel  containing  ammoniacal  liquors,  through 
which  it  bubbles  to  escape  into  funnel-shaped  tubes,  the 
larger  ends  of  which  dip  into  the  liquor  while  the  smaller 
ends  connect  with  the  main  for  the  scrubbed  gas. 

58.  Location  of  Scrubber. — The  location  of  the  scrub¬ 
ber  in  the  condensing  system  varies  in  different  plants. 
In  some  German  works,  it  is  placed  immediately  after  the 
exhauster,  where  the  temperature  is  nearly  that  of  the  dis¬ 
charged  gas,  or  about  65°  to  75°  F.  American  and  English 
practices  agree  in  recommending  that  the  heavy  tar  be 
removed  from  the  gas  before  the  temperature  falls  below 
100°  F.,  since  below  this  temperature  the  tar  absorbs  illumi- 
nants  at  the  expense  of  the  gas.  For  this  reason,  a  better 
location  is  immediately  before  the  final  cooler,  preferably  on 
the  pressure  side  of  the  exhauster,  as  in  this  case  the  some¬ 
what  higher  specific  gravity  of  the  gas  aids  in  the  action. 
One  advantage  of  running  the  Pelouze  &  Audouin  scrubber 
at  the  higher  temperature  is  the  freedom  from  stoppage  of  the 
small  holes  by  naphthalene.  To  facilitate  clearing,  the  bells 
are  frequently  made  polygonal  in  form  instead  of  circular, 
and  the  impinging  plates  bolted  to  the  frame  so  that  they 
can  readily  be  removed  and  clean  ones  substituted  with 
but  little  delay.  A  partial  cleaning  may  be  effected  by 
blowing  in  steam  along  with  the  gas,  but  this  raises  the  gas 


§71 


BY-PRODUCT  COKING 


57 


temperature  and  is  likely  to  interfere  with  the  subsequent 
ammonia  recovery. 

The  presence  of  tar  in  the  gas  passing  from  the  scrubber 
is  detected  by  allowing  a  jet  to  blow  on  white  paper.  If  tar 
is  present,  the  paper  will  be  blackened  immediately;  but  if 
several  minutes’  exposure  produces  no  more  than  a  brown 
stain,  the  gas  is  sufficiently  clean.  If  a  quantitative  determi¬ 
nation  of  the  tar  present  is  desired,  it  can  be  made  by  pass¬ 
ing  the  gas  through  a  weighed  tube  containing  absorbent 
cotton,  then  through  a  meter,  the  increase  in  weight  of  the 
absorption  tube  being  due  to  the  tar  removed  from  the  gas. 
Before  entering  the  absorption  tube,  the  gas  should  be 
freed  from  water  by  being  passed  over  caustic  lime. 


AMMONIA  SCRUBBERS 

59.  The  removal  of  ammonia  vapor  from  the  gas 
depends  on  the  great  absorptive  power  of  water  for 
ammonia.  The  absorption  of  ammonia  is  accomplished  in 
what  are  called  scrubbers,  or  wasliers.  There  are  two 
general  classes  of  ammonia  scrubbers.  In  one  class,  as 
the  seal ,  or  bell ,  scrubbers ,  the  gas  is  forced  by  pressure 
through  successive  seals  dipping  into  water  or  liquor;  in  the 
other  class,  represented  by  the  tower  and  rotary  scrubbers , 
the  gas  is  passed  through  vessels  containing  a  large  amount 
of  wetted  surface,  such  as  in  a  liquor  spray  or  constantly  moist¬ 
ened  steel  plates,  wooden  grids,  gratings  of  parallel  strips 
of  wood,  pieces  of  coke,  or  in  revolving  disks.  The 
objection  to  seal,  or  bell,  scrubbers  is  the  amount  of  work 
they  throw  on  the  exhauster  in  forcing  the  gas  through 
the  seals;  scrubbers  of  the  tower  class  avoid  that  difficulty, 
but  occupy  considerable  space. 

60.  Bell  Washers. — The  seal,  or  bell,  washers  con¬ 
sist,  usually,  of  several  cast-iron  sections  placed  one  above 
the  other  with  the  flanges  bolted  together.  Each  section 
contains  a  certain  depth  of  liquor  and  has  an  opening  for 
the  passage  of  gas  in  its  bottom,  which  opening  is  covered 
by  a  sealing  hood,  which  may  be  quite  simple  or  sometimes 


58 


BY-PRODUCT  COKING 


§71 


very  complicated  in  form.  The  edges  are  usually  saw-tooth 
shaped  and  dip  below  the  liquor  surface.  The  gas  may  pass 
either  upwards  or  downwards,  forcing  its  way  through  the 
seal  and  being  divided  into  fine  bubbles  by  the  toothed  edges. 

The  water  or  liquor  is 
fed  into  the  top  com¬ 
partment  of  the  scrub¬ 
ber,  through  a  seal  of 
sufficient  depth  to  with¬ 
stand  the  pressure  due 
to  the  passage  of  the 
gas  through  the  appara¬ 
tus.  Two  or  more  such 
scrubbers  of  several  sec- 
tions  each  are  usually 
placed  in  series,  the 
compartment  last  trav¬ 
ersed  by  the  gas  being 
fed  with  fresh  water,  in 
order  to  complete  the 
absorption  of  the  ammo¬ 
nia.  The  weak  liquor 
from  the  end  compart¬ 
ments  is  used  in  those 
preceding  them,  and 
thus  strengthened  up  to 
li  to  2a  per  cent,  of 
ammonia  gas,  NH3. 
The  shape  of  the  scrub¬ 
ber  may  be  rectangular, 
circular,  or  octagonal, 
and  the  details  of  its 
construction  differ  with 
Fig.  25  every  design. 


Wafer  or 
Weak  Liquor 


61.  Tower  Scrubbers. — The  tower  scrubber  usually 
consists  of  a  metal  cylinder,  filled  wholly  or  in  part'  with 
some  loose  material  like  coke  or  tile,  or  with  wooden  slats 


§71 


BY-PRODUCT  COKING 


59 


spaced  regularly  and  closely;  the  surfaces  of  this  filling 
material  are  wetted  by  a  constant  spray  of  liquor  or  water 
fed  in  at  the  top  by  some  form  of  sprinkling  device.  In  the 
scrubber  shown  in  Fig.  25,  the  cylinder  a  contains  perforated 
partitions  on  which  coke  or  other  loose  material  is  placed. 
The  water  enters  at  the  top  as  a  spray  through  the  pipe  b. 
In  descending,  it  encounters  the  ascending  gas,  which  enters 
at  the  bottom  through  c  and  passes  out  at  the  top  through  d. 
The  film  of  water  on  the  surfaces  exposed  to  the  gas  absorbs 
the  ammonia  from  it,  forming  ammoniacal  liquor,  which 
passes  out  at  e.  The  best  results  with  such  towers  appear 
to  be  given  by  placing  boards  l  inch  wide  1  inch  apart,  this 
affording  the  greatest  wetted  surface  with  the  least  volume 
to  obstruct  the  gas  passages.  Horizontal  perforated  plates 
placed  at  frequent  intervals  in  the  scrubber,  with  holes  in 
the  plates  i  inch  in  diameter,  thus  forming  a  series  of  plates, 
are  used  in  some  American  plants  with  considerable  success; 
this  latter  form  of  apparatus  is  called  the  sieve  washer.  If 
tower  scrubbers  are  used,  it  is  usually  necessary  to  place 
two  or  more  in  series. 

62.  Horizontal  Rotary  Scrubber. — The  horizontal 
rotary  scrubber,  Fig.  26,  or  washer  scrubber,  as  it  is 
sometimes  termed,  consists  of  a  cast-iron  cylindrical  case  a 
placed  horizontally.  Through  the  axis  runs  a  shaft  b  revolved 
by  the  belt  pulley  c  and  carrying  a  number  of  perforated 
steel  plates,  wooden  grids,  or  brush  wheels,  according  to  the 
particular  type  of  machine.  The  lower  half  of  the  cylinder 
is  filled  with  weak  ammonia  water,  which  wets  the  surface  of 
the  plates  or  grids  as  these  are  slowly  turned  by  the  shaft. 
In  the  type  of  scrubber  shown  in  Fig.  26,  a  number  of  brush 
wheels,  each  having  its  center  filled  with  coke  or  other 
porous  substance  are  mounted  on  the  shaft  b.  The  wheels 
are  so  arranged  that  the  water  is  carried  up  on  the  circum¬ 
ference  of  the  revolving  wheel  and  filters  through  the  per¬ 
forations  shown  in  the  wheel,  keeping  the  coke  thoroughly 
wet.  This  wetted  surface  is  exposed  to  the  action  of  the  gas, 
which  enters  at  d ,  passes  through  the  apparatus  from  end  to 


60 


BY-PRODUCT  COKING 


§71 


end  above  the  water  level,  and  out  at  the  opposite  end.  By 
a  special  arrangement  of  the  plates  or  grids,  in  some  the  gas 
is  made  to  follow  as  tortuous  a  path  as  possible,  in  order  to 
promote  the  absorption  of  ammonia.  When  metal  plates  are 
used,  the  inner  surface  of  the  cylinder  and  the  edges  of  the 
plates  are  machined  so  that  they  come  very  close  to  each 
other  without  actually  touching;  this  allows  the  liquor  to  form 
a  film  joint  in  this  place  and  helps  to  stop  the  gas  from  pass¬ 
ing  through  by  the  shortest  route.  The  main  objection  to  the 
use  of  metal  plates  is  the  great  weight  of  the  moving  parts 
and  the  size  of  shaft  required  to  carry  this  weight  without 
bending.  The  lower  portion  of  the  shell  containing  the 


liquor  is  usually  divided  into  a  number  of  compartments  by 
partitions,  as  shown.  These  compartments  are  connected 
alternately  top  and  bottom  by  openings  in  the  partitions,  so 
that  the  liquor  must  flow  from  one  end  to  the  other,  and  in  this 
way  become  gradually  stronger,  the  fresh  water  or  weakest 
liquor  entering  at  the  end  where  the  gas  is  discharged.  At 
the  bottom  of  each  compartment  are  drain  cocks  for  remov¬ 
ing  any  tar  that  may  gather  there.  The  entering  water  is  fed 
in,  usually,  by  a  small  jet  discharging  into  a  funnel,  which 
extends  sufficiently  high  above  the  liquor  level  inside  to  over¬ 
come  the  pressure  of  the  gas  and  is  provided  with  a  seal  of 
corresponding  depth.  The  discharged  liquor  flows  also 
through  a  sealed  pipe  to  the  liquor  storage  cistern.  The 


§71 


BY-PRODUCT  COKING 


61 


motive  power  is  usually  furnished  by  a  small  upright  steam 
engine  or  an  electric  motor  geared  down  to  give  about  five 
revolutions  per  minute  to  the  main  shaft.  The  whole  appa¬ 
ratus  is  very  compact  and  self-contained  and  requires  little 
power  to  run  it.  It  is  efficient  in  its  operation.  The  main 
objections  to  it  are  that  it  requires  power  for  its  operation  and 
its  initial  cost  is  high.  It  adds  but  a  few  tenths  of  an  inch  to 
the  pressure  of  the  gas  to  be  forced  through  it,  which  advan¬ 
tage,  however,  it  shares  with  most  of  the  scrubbers  of  the 
tower  pattern.  One  pass  through  a  rotary  scrubber  is  usu¬ 
ally  enough  to  absorb  the  ammonia  in  gas  to  within  allowable 
limits,  provided  that  the  quantity  of  gas  passing  through  the 
apparatus  is  not  in  excess  of  its  rated  capacity. 

63.  Ajiparatus  for  Concentrating  tlie  Ammonia. 
The  usual  form  of  concentration  apparatus  is  shown  in 
Fig.  27.  It  consists  of  the  still,  which  includes  two  parts, 
one  a  for  the  ammonia  gas,  known  as  free  ammonia ,  and 
one  b  for  the  ammonium  compounds  known  as  fixed 
ammonia .  Each  part  is  composed  of  cylindrical  cast-iron 
sections  bolted  together  by  flanges,  as  shown,  one  above 
another,  the  sections  being  provided  with  internal  heads  and 
seals.  The  free-ammonia  still  a  discharges  into  the  fixed- 
ammonia  still  b ,  a  lime  chamber  c  being  between  the  two. 
The  weak  liquor  enters  at  the  top  of  the  free-ammonia  still 
from  the  feed-tank  d  and  passes  down  through  the  sections, 
encountering  the  steam,  which  enters  at  the  bottom  of  the 
fixed-ammonia  still  at  e  and  passes  upwards.  The  free 
ammonia  driven  off  by  the  steam  in  the  upper  section  a  and 
that  set  free  by  the  action  of  the  lime  in  c  and  steam  in  the 
fixed-ammonia  section  b  pass  out  through  a  cooler  /,  which 
serves  also  as  a  preheater  for  the  incoming  weak  liquor.  If 
ammonium  sulphate  is  to  be  made,  the  gases  pass  through 
pipes  g  to  the  lead-lined  saturating  boxes  h ,  where  the 
ammonia  is  absorbed  by  the  dilute  sulphuric  acid  placed  in 
them.  The  ammonium  sulphate  is  deposited  in  these  boxes 
in  the  form  of  white  crystals,  accompanied  by  the  evolution  of 
considerable  heat.  When  the  acid  is  sufficiently  neutralized, 
151—26 


§71 


BY-PRODUCT  COKING 


63 


the  contents  of  the  saturators  h  are  discharged  into  the 
cooling  tank  i,  where  the  liquid,  which  is  called  the  mother 
liquor ,  is  cooled  and  drawn  off  to  the  tank  j.  The  sulphate 
is  dried  in  the  centrifugal  drying  machine  k  and  afterwards 
taken  by  the  conveyer  belt  /  to  the  bagging  room. 

If  concentrated  liquor  is  to  be  made,  the  gas  passes 
through  the  pipes  g  to  the  second  cooler  m>  termed  an 
absorber ,  in  which  the  ammonia  and  water  vapors  are  con¬ 
densed  to  a  strong  liquor.  In  either  case,  there  are  certain 
non-condensible  gases  produced  in  the  distillation,  which 
are  obnoxious  in  their  nature  and  are  led  away  by  the  pipe  n 
to  a  smokestack,  or  are  burned  under  the  boilers. 


STORAGE  OF  TAR,  LIQUOR,  AND  GAS 

64.  Amount  of  Storage  Room  Required  for  Tar 
and  Liquor. — It  is  essential  in  a  by-product  coke-oven 
plant  to  provide  ample  storage  room  for  the  tar  and  ammonia 
liquor.  If  the  tar  is  to  be  shipped  direct  to  the  consumer, 
as  is  usually  the  case,  it  is  imperative  that  it  be  given  suffi¬ 
cient  time  to  settle  and  allow  the  entrained  ammoniacal 
liquor  to  separate  from  it.  Otherwise,  this  liquor  will  not 
only  be  lost,  but  cause  complaint  by  the  purchasers.  Steam 
heating  coils  on  the  bottom  of  the  tar  tank  aid  in  the  separa¬ 
tion  of  the  liquor.  Two  weeks  of  quiet  storage  for  settle¬ 
ment  is  by  no  means  a  too  liberal  allowance,  though  good 
results  are  obtained  by  allowing  the  tar  to  flow  by  gravity 
through  three  or  more  steam-heated  vessels  of  moderate 
capacity  so  connected  that  the  heaviest  tar  from  the  first  will 
flow  to  the  second,  which  discharges  its  heaviest  tar  into  the 
third.  In  some  plants,  where  commercial  exigencies  must 
also  be  considered,  storage  for  3  months’  output  is  not  con¬ 
sidered  excessive. 

In  the  case  of  ammoniacal  liquor,  so  much  capacity  is  not 
essential.  In  every  complete  by-product  coke-oven  plant, 
apparatus  for  the  concentration  of  the  weak  liquor  to  strong 
crude  liquor,  or  its  conversion  into  ammonium  sulphate  is 
provided.  The  only  need  for  storage,  therefore,  is  that  the 


64 


BY-PRODUCT  COKING 


§71 


liquor  and  lighter  tars  shall  have  opportunity  to  separate, 
and  for  this  the  storage  of  a  week’s  output  suffices.  This 
may  be  approximated,  as  already  noted,  by  figuring  it  as 
one-quarter  the  weight  of  coal  carbonized  per  day,  for  liquor 
having  1  per  cent,  of  NH3,  or  65  United  States  gallons  per 
ton  of  coal  coked.  As  this  is  a  minimum  strength  for  liquor, 
the  resulting  capacities  should  be  ample.  It  must,  however, 
be  taken  into  account  that  there  are  usually  liquors  of  various 
strengths  made  in  the  condensing  and  scrubbing  processes, 
and  that  the  weaker  liquors  must  be  passed  through  the 
apparatus  again  until  they  are  of  a  proper  strength  for 
economical  concentration.  The  weak  liquors  usually  come 
from  the  first  condensers,  where  the  temperature  is  too  high 
to  permit  of  much  absorption  of  ammonia  in  the  water  that 
is  condensed  from  the  gas,  and  from  the  last  stage  of  the 
washing  process,  where  fresh  water  is  used  for  the  final 
scrubbing.  If  a  rotary  scrubber  is  used,  it  delivers  a  strong, 
crude  liquor,  because  of  the  successive  compartments  through 
which  the  liquor  must  pass,  even  though  it  be  fed  by  fresh 
water.  For  this  reason,  it  is  feasible  to  collect  the  weak 
liquor  from  the  condensers  and  feed  it  into  the  first  few  com¬ 
partments  of  the  rotary  scrubber,  while  fresh  water  is  fed 
into  the  last  compartments  next  the  end  where  the  gas  is 
discharged.  In  this  way,  only  two  grades  of  liquor  need  be 
arranged  for,  the  weak  from  the  condensers  and  the  strong 
from  the  scrubber,  the  latter  liquor  being  pumped  from  the 
overflow  receiver  directly  to  the  main  storage  tank.  Where 
tower  scrubbers  or  seal  washers  are  used,  it  is  necessary  to 
handle  three  or  even  four  strengths  of  liquor,  the  liquor  from 
each  tower  or  set  of  towers  being  kept  separate  and  used  for 
scrubbing  in  the  apparatus  next  preceding.  For  the  sake  of 
convenience  and  reliability  in  operation,  a  certain  amount  of 
the  intermediate  liquors  should  be  kept  on  hand,  so  that 
shut-downs  on  pumps,  etc.  will  not  interrupt  the  work. 

65.  Storage  Cisterns. — The  necessary  storage  cisterns 
are  usually  sunk  beneath  the  ground  level  and  are  built  of 
concrete,  or  brick  laid  in  cement,  with  arched  or  timber  roofs. 


§71 


BY-PRODUCT  COKING 


65 


These  are  convenient,  as  the  tar  and  liquor  will  then  drain 
to  them  directly  from  the  seal  pots  and  apparatus,  and  they 
do  not  take  up  space  above  ground;  but  on  the  other  hand 
they  are  difficult  to  construct  so  that  they  will  not  break,  and 
the  tar  once  in  them  is  harder  to  raise  by  suction  to  the 
pumps  than  if  the  storage  were  above  the  ground  level. 
The  heavier  tar  sinks  to  the  bottom  of  the  cistern  and 
after  a  year  or  two  hardens  to  a  rubbery  substance  that 
will  not  mix  with  the  softer  tar,  and  clogs  the  pumps. 
The  cleaning  out  of  such  a  cistern  underground  is  a 
serious  matter,  whereas  above  ground  it  may  be  drained 
from  time  to  time  and  kept  free  with  little  trouble.  For 
these  reasons,  where  the  cost  is  not  too  great,  a  number 
of  steel  tanks  set  above  ground  seem  to  be  preferable  to  a 
large  underground  cistern  divided  into  sections  by  walls,  for 
the  different  liquids.  It  is,  however,  impossible  to  do  with¬ 
out  some  low-level  cisterns  of  small  capacity  to  receive  the 
drips  from  the  various  seals  and  drains,  but  if  these  are  of 
comparatively  small  size  they  can  be  kept  free  by  pumps, 
and  are  not  hard  to  clean.  Steel  storage  tanks  should  be 
provided  with  bottom  outlets  and  steam  coils  carried  on  sup¬ 
ports  just  above  the  tank  bottom,  so  laid  out  as  to  drain 
any  condensation  to  the  outlet.  A  steam  trap  may  then  be 
placed  at  this  point  and  the  water  thus  removed  without 
further  attention.  If  this  is  not  done,  a  jet  of  steam  must  be 
kept  constantly  blowing  from  the  vent  in  order  to  be  sure 
that  water  is  not  filling  the  pipe.  An  internal  swinging  suc¬ 
tion  pipe  that  may  be  adjusted  to  draw  either  the  upper  liquor 
or  the  lower  tar  is  frequently  used  in  either  steel  or  under¬ 
ground  tanks,  thus  making  only  one  pump  connection  neces¬ 
sary.  Steel  tanks  are  usually  provided  with  self-supporting 
roofs  of  light  plate  with  internal  stays,  though  a  better  plan 
is  to  cover  them  with  a  tight  wooden  roof  covered  with  tar 
and  gravel,  as  the  steel  roof  is  ultimately  attacked  and 
spoiled  by  the  ammonia  fumes,  which  do  not  attack  the 
wood.  The  gravel  or  tin  covering  practically  obviates 
danger  from  fire,  except  from  causes  that  would  be  as 
dangerous  to  a  steel  roof.  The  tighter  it  is  made,  the 


66 


BY-PRODUCT  COKING 


§71 


less  loss  will  there  be  of  ammonia  in  the  form  of  vapor. 
There  should  be  a  manhole  in  the  roof  and  one  near  the 
bottom  of  the  shell,  to  allow  access  for  cleaning  and  repairs. 


66.  Gas  Holders. — In  coke-oven  plants,  when  the  sur¬ 
plus  gas  is  sold  for  outside  purposes,  a  gas  holder,  Fig.  28, 


serves  the  same  purposes  as  it  does  in  the  ordinary  gas  plant, 
that  is,  storage  for  times  of  maximum  consumption  or  mini¬ 
mum  production.  The  amount  of  this  storage  may,  in  gen¬ 
eral,  be  assumed  to  be  24-hours’  production,  though  with 
increased  size  of  plant  and  consequent  multiplication  of 
units,  the  need  for  storage  grows  less.  Local  conditions 
also  influence  this  question  to  a  large  extent.  In  works 
where  the  gas  is  divided  into  two  portions,  a  storage  holder 
of  ample  size  is  usually  essential  for  the  rich  gas.  A  smaller 
holder,  known  as  a  relief  holder ,  is  also  of  great  use  on  the 
poor-gas  system,  as  it  serves  to  regulate  the  pressure  of  the 
oven-heating  gas  and  gives  much  better  results  in  the  oven 
heats.  This  holder  need  not  be  of  great  size,  capacity  for 
i  or  1  hour’s  output  being  sufficient  for  a  plant  not  exceeding 
fifty  ovens,  and  less  in  proportion  for  a  larger  plant.  When 
but  one  grade  of  gas  is  made,  a  holder  is  essential  for  regu¬ 
lating  purposes  and  should  be  installed  at  every  plant, 


§71 


BY-PRODUCT  COKING 


67 


although  it  is  true  that  a  plant  of  moderate  size  can  be  run 
without  a  holder  if  the  coal  used  is  rich  in  gas.  Such  a  plant, 
however,  must  either  waste  a  great  deal  of  its  gas  or  dispose 
of  it  in  some  manner  that  is  not  seriously  affected  by  varia¬ 
tions  in  supply,  if  such  can  be  found.  With  a  coal  low  in 
volatile  matter,  which  soon  yields  its  gas  in  the  oven,  a 
holder  is  necessary  for  the  proper  operation  of  the  plant,  as 
by  its  use  alone  can  the  gas  supply  be  maintained. 

As  the  size,  location,  and  special  conditions  under  which 
each  plant  is  built  vary  widely,  it  is  not  practicable  to  discuss 
the  general  arrangement  more  in  detail.  The  most  useful 
information  in  this  line  may  be  obtained  by  careful  study 
of  the  arrangements  adopted  in  the  various  important  and 
modern  works  like  that  at  Everett,  Massachusetts,  as  shown 
in  Fig.  1. 


' 


•• 

BY-PRODUCT  COKING 


EXAMINATION  QUESTIONS 

(1)  What  is  meant  by  by-product  coking? 

(2)  What  are  the  advantages  of  by-product  coking  over 
coking  in  beehive  ovens? 

(3)  (a)  How  does  the  yield  of  coke  from  by-product 
ovens  compare  with  that  from  beehive  ovens?  ( b )  What  is 
the  cause  of  these  differences? 

(4)  What  important  factors  must  be  taken  into  con¬ 
sideration  in  determining  a  suitable  location  for  a  by-product 
coking  plant? 

(5)  Explain  briefly  the  general  arrangement  of  the  flues 
that  distribute  the  burning  gases  about  the  retort  in  the  Otto- 
Hoffman  oven. 

(6)  (a)  What  provision  is  made  for  preheating  the  air 
for  burning  the  gas  that  heats  the  retorts?  (b)  How  is  the 
heat  maintained  in  these  regenerators? 

(7)  What  advantages  are  there  in  preheating  the  air  for 
the  combustion  of  the  gas? 

(8)  (a)  By  what  indication  can  it  be  known  that  an  oven 
is  burning  properly?  ( b )  What  injury  may  result  if  the 
combustion  in  the  oven  flues  is  not  complete? 

(9)  Explain  how  the  underfired  retort  ovens  differ  from 
the  Otto-Hoffman  ovens  in  principle. 

(10)  What  advantages  do  underfired  retort  ovens  have 
over  end-fired  ovens? 

§71 


151—41 


2  BY-PRODUCT  COKING  §71 

(11)  What  are  the  distinctive  features  of  the  Schniewind 
or  United-Otto  ovens? 

(12)  How  does  the  arrangement  of  the  flues  for  heating 
the  retorts  in  the  Semet-Solvay  oven  differ  from  that  in  the 
Otto-Hoffman  oven? 

(13)  In  what  way  is  the  absence  of  regeneration  offset 
in  the  Semet-Solvay  oven? 

(14)  What  are  the  principal  by-products  obtained  from 
the  gases  from  by-product  ovens? 

(15)  On  what  qualities  does  the  value  of  by-product  gas 
depend? 

(16)  In  what  two  ways  are  gas-collecting  mains  con¬ 
structed  and  in  what  respect  do  they  differ  from  each  other? 

(17)  ( a )  What  two  kinds  of  coolers  are  used  for  con¬ 
densing  the  tar  from  the  hot  gases?  (b)  Explain  the 
principle  of  each. 

(18)  By  what  means  are  the  last  traces  of  tar  removed 
from  the  gas? 

(19)  On  what  principle  does  the  removal  of  ammonia 
from  the  gas  depend? 

(20)  What  are  the  advantages  and  disadvantages  of 
having  storage  cisterns  below  the  ground  level? 

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" 


' 


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82417 


